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how good are class D amplifiers?
In article , Rob
wrote: Jim Lesurf wrote: In article , Rob wrote: snip and surprisingly (to me) there doesn't seem to have been many rigorous tests to underpin the 'little if any difference' thesis. You would need to clarify what you mean as I am unsure of the point you are making. I'll try. 1. It is maintained that most amplifiers sound the same; 2. I haven't see many tests that support (1) That does not seem to me to be the same point as you made above. :-) Nor it is clear to me who "maintains" this as it isn't something I've said. :-) I've seen various people say variations on "well designed and appropriately used" amps give indistinguishable results. But that isn't statement (1). So are you asking for evidence for a claim no-one has made? Is your concern simply that the evidence is based only on all the cases tried? If so, it is open to you or anyone else to collect more evidence. i.e. to carry out more comparison tests of appropriate kinds. To do this you would have to define what you mean by "most". i.e. do you mean more than half of all amps in use, or more than half the designs, or more than half of those ever used, etc? e.g. can we ignore the amps in TVs and portable radios and cheap 'music centers'? If so, we have to define the line that rules in/out a given amp, and give a plausible basis for doing so. You would then have to devise a performable test/experiment and do so on a basis that deals with why you feel all the tests thus far have somehow been 'unrepresentitive' of "most" amplifiers. This means giving a plausible and testable reason for why the previous tests all 'selected' amps such that none of them were in the same alleged catagory as "most" according to your claim. You would then have to *perform* the tests and collect the evidence. There would have to be a statistically significant number of tests and you'd have to be able to establish the level of significance. Then a decision could be based on that *evidence*. If the above isn't done, then your idea is a speculation which the current evidence seems not to support. This puts it into the "teapot orbiting the sun" class. i.e. a fanciful speculation which can't be tested and which the evidence we have shows no sign of supporting. It is easy to make up speculations that remain untested or are essentially intestable. However this means we can invent an infinite number of them which may all conflict. Given this, it seems to me to be a waste of time to take them seriously *unless and until* someone does the above process to find evidence from a test whose outcome had the ability to either conflict or support the idea. I can only point out that "most" (indeed all) the relevant tests I know of showed no sign that those who listened could distinguish one amp from another - given a fairly basic set of requirements like level matching. Interestingly, this includes cases where I and others were quite surprised that those involved *couldn't* distinguish as there were quite large, easily measureable, differences. Indeed, in more than one case the amps compared were deliberately chosen with the aim of being able to find clear differences. Some of the participants chose them for this reason, but then failed when tested to tell one from another. This means that we have in audio a history of people who are confident they can 'hear differences', but when tested fail to show they can hear what they believe. In this context it seems reasonable to be wary of claims - although it is quite clear that some differences are indeed audible, and hence are not contentious. So, for example, tests generally proceed on the basis of level matching as it is generally accepted that a change of level can be audible if reasonably large. Given this, I'd be interested in *evidence* to the effect that it isn't the case that 'most' amps *don't* sound indistinguishable in an appropriate comparison - excepting for reasons which are uncontenious and already understood/accepted. Alas, arguments, discussing the meanings of words, opinions, speculations, etc, aren't evidence Of course, if your point is that 'most' exhibit problems in use like obvious distortions, changes in response, etc, then I can see why you would be concerned. There may well be 'many' amplifiers that produce audibly different results - indeed there are various ways to cause audible changes if we wish. However note the qualifications I have made about what was being compared, and how. However in the absence of evidence I can't see much point in what you are now saying. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html |
how good are class D amplifiers?
In article , Rob
wrote: Jim Lesurf wrote: In article , Rob wrote: Is that simply a 'concept'? I would have regarded it as a description of something which arises in physical reality. 'Concept' seems to me to be a term which sounds more like it was an abstract idea. Yes, that's right - 'distortion' is a concept, and not a thing. You point being that anything we observe in reality and then have a word for is a 'concept'? Does that approach serve any purpose when we are trying to deal with reality? It seems to me to be no more than playing with words and doing this as a replacement for dealing with reality. In effect, a displacement acitivity. and not a single or pejorative (in the context of valves discussions say) fact. Pejorative would be 'in the ear of the belistener' I guess. :-) Quite! If (and I say 'if'; I don't know) distortion is the cause of what I consider to be the 'accurate' sound I get from a valve amplifier and LPs then it's beneficial. That is OK for you as an individial if you are making up your own meaning of 'accurate', etc. The problems arise as soon as you try to communicate with the rest of us since you are using the Lewis Carroll version. :-) Afraid you have to make decide which you prefer. Playing with words and confusing the issues, or dealing with reality and being able to communicate with others. The reality, though, is that if the output has a nonlinear relation to the input then it is a 'fact' that the result is being distorted according to the relevant definitions. This can be measured, and may be audible, depending on circumstances. Whether someone likes or dislikes (or can even tell the difference) the results is up to them. Of course, I'd like them to be able to make an 'informed' choice - hence my previous comments. But that isn't compulsory... ;- Yes. I think it may follow that you're led my measurement and I'm led by the sound I hear. ....or it may not. :-) False and inappropriate dichotomy. :-) Actually I've been trying to point out that I am not 'led' by either in isolation. I try to be guided or informed by both, and try to be so in a way that is appropriate for the relevant situations or issue. That's fine in the main, of course - it's your world and it suits you (and probably many others). I'm not so happy, though, with lumping enthusiastic commentary and enquiring minds in with 'wilful ignorance', which I'm afraid is how I read the essence of what you seem to be saying. Why are you assuing that enthusiam and enquiry mean wilifil ignorance? I'd have said the exact opposite. I'm afraid that you are reading into what I wrote something that I neither said not meant. You skip from 'nonlinear' audio to 'informed choice' to 'unfounded claims' to 'wilful ignorance'. I do the first three, but don't consider myself wilfully ignorant. Delusional but happy maybe :-) The 'wilful ignorance' arises when people don't want to know about any measurements or to understand the relevant physics, etc. The 'ignorance' part comes from them not knowing the measured results or having any understanding of them. The 'wilful' comes from this being a result of their deliberate choice, not from not knowing measurements can be made and their meanings understood. Of course, that's fine if it keeps one 'happy' but it may mean that any comments they made beyond that are worthless for anyone else, and may simply mislead or confuse. It is perfectly reasonable for someone to decide to remain ignorant about some topic. There are many topics in which each of us have no interest. However this means our views on such topics may be worthless. The bit where I would go along (in part at least) with your obviously strong and informed opinions on this arise around the 'unfounded claim', and the extent to which the adherent rams it down somebody else's throat. But then I don't think an unfounded claim is incorrect, or ignorant - wilful or otherwise. in physical science and engineering 'unfounded' does not simply mean there is no evidence or plausible argument consistent with what has been established. Ideas for which there is no evidence one way or another, and which can't be assessed for consistency are 'untested' and/or 'unassessed' not 'unfounded'. Such ideas remain speculations and may be void of value *until* tested, etc. An 'unfounded' claim is one which clashes with established physics (i.e. clashes with the evidence which it describes) or is simply confounded by directly relevant experimental evidence. If you wish to continue to accept such ideas, you are free to do so, but so far as science is concerned it then becomes an 'article of faith' on your part, nothing to do with science. An 'enquiring mind' would seek to *understand* what they experience - and also seek to check if their impressions or ideas have any reliability or are errors. Enthusiam is one of the things that can drive this. OK, no doubt. 'Understanding' is, again, conceptual. Again you seem fonder of playing with words than with dealing with the reality. :-) The point of 'understanding' is that it allows you to deal correctly with reality. i.e. you can then design, analyse, predict, etc, and find that things do behave as intended in cases that were not identical with your original evidence. The 'understanding' is evidence based and tested by proving successful in such ways - or is discarded/altered as appropriate. Is it 'conceptual' that when you build a bridge it does not collapse the next day? If you think so, then your meaning of the word differs from mine. I would also be reluctant to employ you to build bridges, or walk on/under any you designed. :-) And here I think it's important to define your paradigm. I work in an applied social science department, That may be the reason for your approach and the source of some of the inappropriate nature of some of your arguments/definitions on this group... :-) I'm afraid that 'social science' is not a 'science' in the same sense as physics or engineering, and may well use terms or arguments in a quite different way. Thus your background may simply be causing you problems with understanding what I and other have been explaining. FWIW The main reason I've spent decades studying, building, testing, etc, audio amplifiers and other kit is that I am largely driven by my enthusiasm for the results - being able to enjoy the music. My point, therefore, was that measurements, etc, are very valuable (if you understand them), and allow you to make more progress. And modesty no doubt forbids the qualification: 'measurement is not all' :-) No idea why you wrote that. Being able to make measurements and analyse designs, etc, does not prevent you from also listening to the results. There is no inherent dichotomy here. Of course. If there is a problem it is in the area I referred to. Which remains a tad fuzzy. To you. :-) if you really want to make more sense of this it would probably be best if you did spent some time studying physical science and engineering. And in learning the scientific method, and the related topics of experimental design in physical sciences, etc. As it is, your background may be causing you some confusion. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html |
how good are class D amplifiers?
"Arny Krueger" wrote in message ... "Keith G" wrote in message "Arny Krueger" wrote in message . .. "Keith G" wrote in message "Arny Krueger" wrote in message . .. "Rob" wrote in message Yes, I agree. DBT is not a trivial thing though, and surprisingly (to me) there doesn't seem to have been many rigorous tests to underpin the 'little if any difference' thesis. What would constitute many? I've done DBTs of several dozen hi fi power amps, and found near-total support for the "little if any difference" thesis. Sure, of course - and it would be stunning if it weren't for the fact that, in a domestic environment, most people couldn't tell the difference between two pieces of kit after a couple of goes back and forth - even if *they* were making the switches fully sighted!! Yet another irrelevant statement from a member of the "great unwashed". The relevance problem here is that the evaluations I'm talking about have been vastly more extensive than "a couple of goes back and forth". The relevance problem here is yours, squire - how many people here have actually *witnessed* a DBT, Thousands and thousands of audiophiles. let alone conducted one? Thousands and thousands of audiophiles, courtesty of www.pcabx.com and numerous sites like it. Aha! Thought so..... :-) |
how good are class D amplifiers?
"Arny Krueger" wrote in message . .. "Dave Plowman (News)" wrote in message In article , Keith G wrote: "Arny Krueger" wrote in message . .. "Rob" wrote in message [snip] I've done DBTs of several dozen hi fi power amps, I actually doubt that.... Why? Personal bias. Nope, call it *real world* experience.... |
how good are class D amplifiers?
"Arny Krueger" wrote in message . .. "Keith G" wrote in message "Arny Krueger" wrote in message . .. "Rob" wrote in message Yes, I agree. DBT is not a trivial thing though, and surprisingly (to me) there doesn't seem to have been many rigorous tests to underpin the 'little if any difference' thesis. What would constitute many? I've done DBTs of several dozen hi fi power amps, I actually doubt that.... Your track record for being wrong at just about every turn is unmolested, Keith. Sadly, all too often these days, but not in the case of knowing when 'several' usually means *two* and 'several dozen' probably means either less than 5 or no *real* ones at all... |
how good are class D amplifiers?
"Keith G" wrote in message
"Arny Krueger" wrote in message . .. "Keith G" wrote in message "Arny Krueger" wrote in message . .. "Rob" wrote in message Yes, I agree. DBT is not a trivial thing though, and surprisingly (to me) there doesn't seem to have been many rigorous tests to underpin the 'little if any difference' thesis. What would constitute many? I've done DBTs of several dozen hi fi power amps, I actually doubt that.... Your track record for being wrong at just about every turn is unmolested, Keith. Sadly, all too often these days, but not in the case of knowing when 'several' usually means *two* and 'several dozen' probably means either less than 5 or no *real* ones at all... That would be your problem, Keith. I currently own or have ready access to about a dozen power amps. Just one audio system of mine has 3 power amps. Then there are the ones I borrow. For just one amplifier auditioning session, a friend who is a well-known magazine reviewer brought over about another half dozen power amps that he had laying around. Then there are the ones that belong to other people in our Hi Fi club, only a fraction of which are listed on the web. |
how good are class D amplifiers?
"Arny Krueger" wrote in message ... "Keith G" wrote in message "Arny Krueger" wrote in message . .. "Keith G" wrote in message "Arny Krueger" wrote in message . .. "Rob" wrote in message Yes, I agree. DBT is not a trivial thing though, and surprisingly (to me) there doesn't seem to have been many rigorous tests to underpin the 'little if any difference' thesis. What would constitute many? I've done DBTs of several dozen hi fi power amps, I actually doubt that.... Your track record for being wrong at just about every turn is unmolested, Keith. Sadly, all too often these days, but not in the case of knowing when 'several' usually means *two* and 'several dozen' probably means either less than 5 or no *real* ones at all... That would be your problem, Keith. I currently own or have ready access to about a dozen power amps. Just one audio system of mine has 3 power amps. Then there are the ones I borrow. For just one amplifier auditioning session, a friend who is a well-known magazine reviewer brought over about another half dozen power amps that he had laying around. Then there are the ones that belong to other people in our Hi Fi club, only a fraction of which are listed on the web. That there may be a grain of truth in your reply is at once the most hilarious and most disturbing aspects of what you claim. But you are talking to the wrong person anyway, because.... ....because... ....because after lunch the Pixie Truck is coming here and it will be dropping off, ooh, probably *400* power amps for me to DBT.... ('Hi Fi Club' ?? - Where TF did that spring from...???) |
how good are class D amplifiers?
"Keith G" wrote in message
('Hi Fi Club' ?? - Where TF did that spring from...???) It's been around since the mid 1970s: http://www.provide.net/~djcarlst/smwtms.htm http://groups.google.com.my/group/re...a655085a0f7586 |
how good are class D amplifiers?
"Rob" wrote in message
Arny Krueger wrote: "Rob" wrote in message Yes, we've done this, and I set out a few problems I had with your methodology and method. I've reviewed the last 100 or so google summaries of your posts here, and can't find any such thing. Can you give me a range of dates or something? 6 Nov 06 - here's a snippet (I keep changing my email 'code' for reasons unknown): Steven Sullivan wrote: In rec.audio.tech Arny Krueger wrote: "Jim Lesurf" wrote in message In article , Rob wrote: Jim Lesurf wrote: In article , Rob wrote: What exactly is the ontological and epistemological basis of the 'virtual reality' methodology? I have to be absolutely clear on these points to accept what you say. Nice job of raising the bar to impossible heights. I've seen this technique used many times before and I'm not playing. Well, it's your ball :-) Same basic answer - questions like this were actually interesting to some people back in the late 1970s and early 1980s. A guy named Daniel Shanefield (AKA Daniel Sheffield) discussed them quite extensively in the BAS Speaker, Audio Magazine, and Stereo Review. http://www.bostonaudiosociety.org/ba...iniscences.htm "I forgot to mention a philosophical thought that might be of interest to some of the members: any scientific principles that are first published in the BASS, if they are later verified by other researchers and if they prove to be broadly useful, will live pretty much forever-or at least as long as there is civilization. Not only do these new principles then get existences of their own, spreading almost like living beings, but in many cases a trail of "literature references" builds up, which brings a certain level of fame and glory to the original publications. (You can see by my use of the word "glory" that I take these things seriously!) However, I don't think that is exaggerated, when it involves a big battle between truth and untruth, or if a new methodology is made available that will help future designers innovate better equipment for all of us.) "One example is the equalized double-blind (d-b) listening test, which was first suggested in my BASS article of November 1974, with results of such a test then reported in June 1975, and with a further summary appearing in January 1976. That seems like a long time ago, but scientists tend to keep meticulous track of these things, partly to give credit wherever it is due (including a legal necessity for the worldwide patent system), but also to aid in the important task of keeping a network of tricky ideas nicely straightened out for all to see (and maybe improve upon later). "The trail of the now famous (or infamous) d-b test can be traced through an article by BAS member Stanley Lip****z, who has been president of the Audio Engineering Society (AES). Lip****z, with John Vanderkooy, wrote about the d-b test in the Journal of the AES (July 1981). This detailed article listed 10 previous BASS articles on the subject, starting with my 1974 piece. A lively discussion, by Lip****z and me and others, of some of the ideas (mostly relating to the audibility of polarity) was then printed in the JAES (June 1983). The trail was marked further when BAS member Les Leventhal explained improvements in the understanding of d-b statistics (JAES, June 1986). And even as recently as April 1994, BAS member Dick Greiner (with Douglas Melton) wrote further about polarity in the JAES and dutifully referred to the 1983 discussion mentioned above, in which I had invoked some blind-testing reports in the BASS while trying to prove a point. So, as you can see, printed references to these BASS moldy oldies continue into the '90s. http://www.aes.org/e-lib/browse.cfm?elib=5549 |
how good are class D amplifiers?
"Arny Krueger" wrote in message . .. "Keith G" wrote in message ('Hi Fi Club' ?? - Where TF did that spring from...???) It's been around since the mid 1970s: http://www.provide.net/~djcarlst/smwtms.htm http://groups.google.com.my/group/re...a655085a0f7586 OK, OK, I give in!! Go on then - I'll take a dozen, but no *bruised* ones mind.... (First we get the smoke, then we get the mirrors!! :-)) |
how good are class D amplifiers?
Jim Lesurf wrote:
In article , Rob wrote: Jim Lesurf wrote: In article , Rob wrote: snip and surprisingly (to me) there doesn't seem to have been many rigorous tests to underpin the 'little if any difference' thesis. You would need to clarify what you mean as I am unsure of the point you are making. I'll try. 1. It is maintained that most amplifiers sound the same; 2. I haven't see many tests that support (1) That does not seem to me to be the same point as you made above. :-) Point 1 is the 'little if any difference' reference. It's related to a reference Serge Aukland made applicable 'most modern amplifiers'(1). Point 2 is a reference to 'many tests'. There are two points - not one. Nor it is clear to me who "maintains" this as it isn't something I've said. :-) I would never attribute you with anything quite so unequivocal :-) I've seen various people say variations on "well designed and appropriately used" amps give indistinguishable results. But that isn't statement (1). So are you asking for evidence for a claim no-one has made? Nope - see above. Is your concern simply that the evidence is based only on all the cases tried? If so, it is open to you or anyone else to collect more evidence. i.e. to carry out more comparison tests of appropriate kinds. My concern (such as it is) is simply this: I maintain different modern SS amplifiers can sound different. They are particularly affected by load (speakers) in my extraordinarily humble opinion. Others (on this NG, not you explicitly so far as I can tell) maintain this is highly unlikely. For example, I'm pretty sure I could hear the difference between a Cambridge audio power amp, a semi-pro power amp, and a Quad 405 power amp. To do this you would have to define what you mean by "most". i.e. do you mean more than half of all amps in use, or more than half the designs, or more than half of those ever used, etc? e.g. can we ignore the amps in TVs and portable radios and cheap 'music centers'? If so, we have to define the line that rules in/out a given amp, and give a plausible basis for doing so. Again, Serge guided me on this. This issue has been mentioned many times. 'Most' means virtually all modern SS amps that meet certain criteria (1). You would then have to devise a performable test/experiment and do so on a basis that deals with why you feel all the tests thus far have somehow been 'unrepresentitive' of "most" amplifiers. This means giving a plausible and testable reason for why the previous tests all 'selected' amps such that none of them were in the same alleged catagory as "most" according to your claim. You would then have to *perform* the tests and collect the evidence. There would have to be a statistically significant number of tests and you'd have to be able to establish the level of significance. Yes, I understand that's necessary if you're going to take notice of anything I say. Then a decision could be based on that *evidence*. If the above isn't done, then your idea is a speculation which the current evidence seems not to support. This puts it into the "teapot orbiting the sun" class. i.e. a fanciful speculation which can't be tested and which the evidence we have shows no sign of supporting. It is easy to make up speculations that remain untested or are essentially intestable. However this means we can invent an infinite number of them which may all conflict. Given this, it seems to me to be a waste of time to take them seriously *unless and until* someone does the above process to find evidence from a test whose outcome had the ability to either conflict or support the idea. I can only point out that "most" (indeed all) the relevant tests I know of showed no sign that those who listened could distinguish one amp from another - given a fairly basic set of requirements like level matching. I find this virtually impossible to do, even (or because of?) the crude sound meter I have. I assume the idea is to match levels between 20-20K Hz? Interestingly, this includes cases where I and others were quite surprised that those involved *couldn't* distinguish as there were quite large, easily measureable, differences. Indeed, in more than one case the amps compared were deliberately chosen with the aim of being able to find clear differences. Some of the participants chose them for this reason, but then failed when tested to tell one from another. This means that we have in audio a history of people who are confident they can 'hear differences', but when tested fail to show they can hear what they believe. In this context it seems reasonable to be wary of claims - although it is quite clear that some differences are indeed audible, and hence are not contentious. So, for example, tests generally proceed on the basis of level matching as it is generally accepted that a change of level can be audible if reasonably large. That I maintain there's a difference doesn't mean there is one. It's quite simple - if I didn't think there was a difference I wouldn't have so many SS amplifiers! Until about 10 years ago I only ever had one at any one time (with a bit of overlap) - heightened awareness has arisen with Dynaudio speakers. Given this, I'd be interested in *evidence* to the effect that it isn't the case that 'most' amps *don't* sound indistinguishable in an appropriate comparison - excepting for reasons which are uncontenious and already understood/accepted. Alas, arguments, discussing the meanings of words, opinions, speculations, etc, aren't evidence Of course, if your point is that 'most' exhibit problems in use like obvious distortions, changes in response, etc, then I can see why you would be concerned. There may well be 'many' amplifiers that produce audibly different results - indeed there are various ways to cause audible changes if we wish. However note the qualifications I have made about what was being compared, and how. However in the absence of evidence I can't see much point in what you are now saying. Okeydokey. Rob (1) This was Serge's reply to my question 'what's necessary to ensure two amps sound the same': Here is my understanding of the threshold levels:- Distortions - all types, THD, IMD 0.1% Important Note: This distortion is measured from 20Hz to 20kHz with a bandwidth of 100kHz, and must be maesured into the loads declared suitable by the designer. For example, the QUAD 405 is rated at 100watts into any load 4-8 ohms. Consequently, I would expect it to work with loudspeakers rated at 6 ohms upwards. Note that 4 ohm rated loudspeakers can drop to 3.2 ohms, and would consequently fall outside QUAD's specification for the 405. Frequency response +-1dB 20Hz-20kHz Important note: This frequency response is measured across the loudspeaker load, *not* across a dummy load. This requires the amplifier to have a low output impdeance as otherwise, the loudspeaker's impedance characteristic will modify the frequency response. Hum and noise 80dB measured on a bandwidth of 20Hz-20kHz, and no worse than -60dB outside that band. It is important that the amplifier have no instabilities at sub or supersonic frequencies. Crosstalk: 60dB In practice, crosstalk below -40dB is unlikely to be audible under programme conditions. It is important that the distortion of the crosstalk be below 0.1% as otherwise, the crosstalk distortion could swamp the speaking channel's distortion. This is a rare condition, but not unknown with poor designs with poor power-supply rejection. |
how good are class D amplifiers?
Jim Lesurf wrote:
In article , Rob wrote: Jim Lesurf wrote: In article , Rob wrote: Is that simply a 'concept'? I would have regarded it as a description of something which arises in physical reality. 'Concept' seems to me to be a term which sounds more like it was an abstract idea. Yes, that's right - 'distortion' is a concept, and not a thing. You point being that anything we observe in reality and then have a word for is a 'concept'? No, cheese is a thing, distortion is a concept. Does that approach serve any purpose when we are trying to deal with reality? It seems to me to be no more than playing with words and doing this as a replacement for dealing with reality. In effect, a displacement acitivity. I'd rather dispense with the word distortion TBH. and not a single or pejorative (in the context of valves discussions say) fact. Pejorative would be 'in the ear of the belistener' I guess. :-) Quite! If (and I say 'if'; I don't know) distortion is the cause of what I consider to be the 'accurate' sound I get from a valve amplifier and LPs then it's beneficial. That is OK for you as an individial if you are making up your own meaning of 'accurate', etc. The problems arise as soon as you try to communicate with the rest of us since you are using the Lewis Carroll version. :-) Still, I'd (kind of) like to know why valves/vinyl sounds better. For techie types I think the term is 2nd harmonic distortion? Afraid you have to make decide which you prefer. Playing with words and confusing the issues, or dealing with reality and being able to communicate with others. I don't follow - what choices am I allowed? The reality, though, is that if the output has a nonlinear relation to the input then it is a 'fact' that the result is being distorted according to the relevant definitions. This can be measured, and may be audible, depending on circumstances. Whether someone likes or dislikes (or can even tell the difference) the results is up to them. Of course, I'd like them to be able to make an 'informed' choice - hence my previous comments. But that isn't compulsory... ;- Yes. I think it may follow that you're led my measurement and I'm led by the sound I hear. ...or it may not. :-) Blimey, 'ere we go. Only you know! False and inappropriate dichotomy. :-) .... *may* follow, *approximate* trend. Actually I've been trying to point out that I am not 'led' by either in isolation. I try to be guided or informed by both, and try to be so in a way that is appropriate for the relevant situations or issue. Good, that's good. That's fine in the main, of course - it's your world and it suits you (and probably many others). I'm not so happy, though, with lumping enthusiastic commentary and enquiring minds in with 'wilful ignorance', which I'm afraid is how I read the essence of what you seem to be saying. Why are you assuing that enthusiam and enquiry mean wilifil ignorance? I'd have said the exact opposite. I'm afraid that you are reading into what I wrote something that I neither said not meant. You skip from 'nonlinear' audio to 'informed choice' to 'unfounded claims' to 'wilful ignorance'. I do the first three, but don't consider myself wilfully ignorant. Delusional but happy maybe :-) The 'wilful ignorance' arises when people don't want to know about any measurements or to understand the relevant physics, etc. The 'ignorance' part comes from them not knowing the measured results or having any understanding of them. The 'wilful' comes from this being a result of their deliberate choice, not from not knowing measurements can be made and their meanings understood. Of course, that's fine if it keeps one 'happy' but it may mean that any comments they made beyond that are worthless for anyone else, and may simply mislead or confuse. It is perfectly reasonable for someone to decide to remain ignorant about some topic. There are many topics in which each of us have no interest. I tend to find interest in just about everything, except sport for some reason. However this means our views on such topics may be worthless. Or amusing (etc) - depends how they're put across. The bit where I would go along (in part at least) with your obviously strong and informed opinions on this arise around the 'unfounded claim', and the extent to which the adherent rams it down somebody else's throat. But then I don't think an unfounded claim is incorrect, or ignorant - wilful or otherwise. in physical science and engineering 'unfounded' does not simply mean there is no evidence or plausible argument consistent with what has been established. Ideas for which there is no evidence one way or another, and which can't be assessed for consistency are 'untested' and/or 'unassessed' not 'unfounded'. Such ideas remain speculations and may be void of value *until* tested, etc. An 'unfounded' claim is one which clashes with established physics (i.e. clashes with the evidence which it describes) or is simply confounded by directly relevant experimental evidence. If you wish to continue to accept such ideas, you are free to do so, but so far as science is concerned it then becomes an 'article of faith' on your part, nothing to do with science. I still think the 'amplifiers don't sound the same' hypothesis is interesting, worthwhile and (of course) grossly irritating round these parts. An 'enquiring mind' would seek to *understand* what they experience - and also seek to check if their impressions or ideas have any reliability or are errors. Enthusiam is one of the things that can drive this. OK, no doubt. 'Understanding' is, again, conceptual. Again you seem fonder of playing with words than with dealing with the reality. :-) The point of 'understanding' is that it allows you to deal correctly with reality. i.e. you can then design, analyse, predict, etc, and find that things do behave as intended in cases that were not identical with your original evidence. The 'understanding' is evidence based and tested by proving successful in such ways - or is discarded/altered as appropriate. Is it 'conceptual' that when you build a bridge it does not collapse the next day? If you think so, then your meaning of the word differs from mine. I would also be reluctant to employ you to build bridges, or walk on/under any you designed. :-) And you'd be wise beyond your years :-) And here I think it's important to define your paradigm. I work in an applied social science department, That may be the reason for your approach and the source of some of the inappropriate nature of some of your arguments/definitions on this group... :-) What we're dealing with is a moment of interaction - if you abandon human experience and discount interaction, then I agree wholeheartedly. I'm afraid that 'social science' is not a 'science' in the same sense as physics or engineering, and may well use terms or arguments in a quite different way. Thus your background may simply be causing you problems with understanding what I and other have been explaining. May well. It's applied social science by the way. FWIW The main reason I've spent decades studying, building, testing, etc, audio amplifiers and other kit is that I am largely driven by my enthusiasm for the results - being able to enjoy the music. My point, therefore, was that measurements, etc, are very valuable (if you understand them), and allow you to make more progress. And modesty no doubt forbids the qualification: 'measurement is not all' :-) No idea why you wrote that. You place great store in positivist data. Yet you consider the human response to that data as significant. 'Sounds rubbish' is not an example of positivist data. Measurement is not all - you know that, but didn't feel the need to say it. Being able to make measurements and analyse designs, etc, does not prevent you from also listening to the results. There is no inherent dichotomy here. Of course. If there is a problem it is in the area I referred to. Which remains a tad fuzzy. To you. :-) if you really want to make more sense of this it would probably be best if you did spent some time studying physical science and engineering. And in learning the scientific method, and the related topics of experimental design in physical sciences, etc. As it is, your background may be causing you some confusion. It may. Rob |
how good are class D amplifiers?
"Rob" wrote in message ... Jim Lesurf wrote: In article , Rob wrote: Jim Lesurf wrote: In article , Rob wrote: snip and surprisingly (to me) there doesn't seem to have been many rigorous tests to underpin the 'little if any difference' thesis. You would need to clarify what you mean as I am unsure of the point you are making. I'll try. 1. It is maintained that most amplifiers sound the same; 2. I haven't see many tests that support (1) That does not seem to me to be the same point as you made above. :-) Point 1 is the 'little if any difference' reference. It's related to a reference Serge Aukland made applicable 'most modern amplifiers'(1). Point 2 is a reference to 'many tests'. There are two points - not one. Nor it is clear to me who "maintains" this as it isn't something I've said. :-) I would never attribute you with anything quite so unequivocal :-) I've seen various people say variations on "well designed and appropriately used" amps give indistinguishable results. But that isn't statement (1). So are you asking for evidence for a claim no-one has made? Nope - see above. Is your concern simply that the evidence is based only on all the cases tried? If so, it is open to you or anyone else to collect more evidence. i.e. to carry out more comparison tests of appropriate kinds. My concern (such as it is) is simply this: I maintain different modern SS amplifiers can sound different. They are particularly affected by load (speakers) in my extraordinarily humble opinion. Others (on this NG, not you explicitly so far as I can tell) maintain this is highly unlikely. For example, I'm pretty sure I could hear the difference between a Cambridge audio power amp, a semi-pro power amp, and a Quad 405 power amp. To do this you would have to define what you mean by "most". i.e. do you mean more than half of all amps in use, or more than half the designs, or more than half of those ever used, etc? e.g. can we ignore the amps in TVs and portable radios and cheap 'music centers'? If so, we have to define the line that rules in/out a given amp, and give a plausible basis for doing so. Again, Serge guided me on this. This issue has been mentioned many times. 'Most' means virtually all modern SS amps that meet certain criteria (1). You would then have to devise a performable test/experiment and do so on a basis that deals with why you feel all the tests thus far have somehow been 'unrepresentitive' of "most" amplifiers. This means giving a plausible and testable reason for why the previous tests all 'selected' amps such that none of them were in the same alleged catagory as "most" according to your claim. You would then have to *perform* the tests and collect the evidence. There would have to be a statistically significant number of tests and you'd have to be able to establish the level of significance. Yes, I understand that's necessary if you're going to take notice of anything I say. Then a decision could be based on that *evidence*. If the above isn't done, then your idea is a speculation which the current evidence seems not to support. This puts it into the "teapot orbiting the sun" class. i.e. a fanciful speculation which can't be tested and which the evidence we have shows no sign of supporting. It is easy to make up speculations that remain untested or are essentially intestable. However this means we can invent an infinite number of them which may all conflict. Given this, it seems to me to be a waste of time to take them seriously *unless and until* someone does the above process to find evidence from a test whose outcome had the ability to either conflict or support the idea. I can only point out that "most" (indeed all) the relevant tests I know of showed no sign that those who listened could distinguish one amp from another - given a fairly basic set of requirements like level matching. I find this virtually impossible to do, even (or because of?) the crude sound meter I have. I assume the idea is to match levels between 20-20K Hz? Interestingly, this includes cases where I and others were quite surprised that those involved *couldn't* distinguish as there were quite large, easily measureable, differences. Indeed, in more than one case the amps compared were deliberately chosen with the aim of being able to find clear differences. Some of the participants chose them for this reason, but then failed when tested to tell one from another. This means that we have in audio a history of people who are confident they can 'hear differences', but when tested fail to show they can hear what they believe. In this context it seems reasonable to be wary of claims - although it is quite clear that some differences are indeed audible, and hence are not contentious. So, for example, tests generally proceed on the basis of level matching as it is generally accepted that a change of level can be audible if reasonably large. That I maintain there's a difference doesn't mean there is one. It's quite simple - if I didn't think there was a difference I wouldn't have so many SS amplifiers! Until about 10 years ago I only ever had one at any one time (with a bit of overlap) - heightened awareness has arisen with Dynaudio speakers. Given this, I'd be interested in *evidence* to the effect that it isn't the case that 'most' amps *don't* sound indistinguishable in an appropriate comparison - excepting for reasons which are uncontenious and already understood/accepted. Alas, arguments, discussing the meanings of words, opinions, speculations, etc, aren't evidence Of course, if your point is that 'most' exhibit problems in use like obvious distortions, changes in response, etc, then I can see why you would be concerned. There may well be 'many' amplifiers that produce audibly different results - indeed there are various ways to cause audible changes if we wish. However note the qualifications I have made about what was being compared, and how. However in the absence of evidence I can't see much point in what you are now saying. Okeydokey. Rob (1) This was Serge's reply to my question 'what's necessary to ensure two amps sound the same': Here is my understanding of the threshold levels:- Distortions - all types, THD, IMD 0.1% Important Note: This distortion is measured from 20Hz to 20kHz with a bandwidth of 100kHz, and must be maesured into the loads declared suitable by the designer. For example, the QUAD 405 is rated at 100watts into any load 4-8 ohms. Consequently, I would expect it to work with loudspeakers rated at 6 ohms upwards. Note that 4 ohm rated loudspeakers can drop to 3.2 ohms, and would consequently fall outside QUAD's specification for the 405. Frequency response +-1dB 20Hz-20kHz Important note: This frequency response is measured across the loudspeaker load, *not* across a dummy load. This requires the amplifier to have a low output impdeance as otherwise, the loudspeaker's impedance characteristic will modify the frequency response. Hum and noise 80dB measured on a bandwidth of 20Hz-20kHz, and no worse than -60dB outside that band. It is important that the amplifier have no instabilities at sub or supersonic frequencies. Crosstalk: 60dB In practice, crosstalk below -40dB is unlikely to be audible under programme conditions. It is important that the distortion of the crosstalk be below 0.1% as otherwise, the crosstalk distortion could swamp the speaking channel's distortion. This is a rare condition, but not unknown with poor designs with poor power-supply rejection. Rob, Are you saying that even with two amplifiers meeting the above criteria you can hear a difference or that you can hear differences between amplifiers that may or may not meet the above criteria, you just don't know as you haven't made the measurements? If the former, then we should look into ths further, as it would be a valuable addition to our knowledge. If the latter, then of course, amplifiers with different performance characteristics can sound different. If any of the above criteria are not met, and the most obvious are level matching and frequency response differences, then in all probability they will sound different because they are. Level matching needs to be done carefully, and can only be valid if the frequency response of the two amplifiers is checked first, and found to be within +_1dB *of each other* into the loudspeaker load being used. Once differences are identified and quantified, then any audible differences are soon accounted for. What I am saying is that with modern SS amplifiers, it is easy except at the very cheapest end for the above criteria to be met, consequently any but the cheapest amps will all sound the same when played at the same volume into the same (sensible) load. The same applies to CD players and anything else that meets the criteria. Items that don't meet the criteria (rarely or never) are transducers and consequently microphones, pick-up cartridges and loudspeakers will all sound different for easily identified and measurable reasons. S. -- http://audiopages.googlepages.com |
how good are class D amplifiers?
"Rob" wrote in message
My concern (such as it is) is simply this: I maintain different modern SS amplifiers can sound different. Of course they can. One popular means is to play them so that they result in different SPLs. Another popular means is to give people a quick talk about how superior one or inferior the other is, and then demonstrate them as such. They are particularly affected by load (speakers) in my extraordinarily humble opinion. One who claims to be more humble than others, is obviously not truely humble at all. Good amplifiers are designed to be as resistant as is reasonably possible to being affected by their loads. This goal is frequently met. Others (on this NG, not you explicitly so far as I can tell) maintain this is highly unlikely. For example, I'm pretty sure I could hear the difference between a Cambridge audio power amp, a semi-pro power amp, and a Quad 405 power amp. Why would this even be of interest? I thought that audio is related to the love of music, not the peculiarities of amplifiers. |
how good are class D amplifiers?
In article , Rob
wrote: Jim Lesurf wrote: Is your concern simply that the evidence is based only on all the cases tried? If so, it is open to you or anyone else to collect more evidence. i.e. to carry out more comparison tests of appropriate kinds. My concern (such as it is) is simply this: I maintain different modern SS amplifiers can sound different. It is essentially self-evident that they 'can'. Indeed, you can choose to design two amps so that they do. However when people have done tests on amps that were not specifically designed to do this and which were designed to amplify, then they tend to be able to distinguishg one from another. i.e. they are found not to 'sound different'. But if you choose a design which is - either by deliberate choice or incompetence - making the output sufficiently different from a scaled version of the input then it may well 'sound different'. They are particularly affected by load (speakers) in my extraordinarily humble opinion. Others (on this NG, not you explicitly so far as I can tell) maintain this is highly unlikely. For example, I'm pretty sure I could hear the difference between a Cambridge audio power amp, a semi-pro power amp, and a Quad 405 power amp. Well you may be "pretty sure", but the problem is that many people in the past have been "pretty sure" of similar claims - but then failed to be able to do what they were "pretty sure" of when tested on the basis of the sounds in a matter that excluded well known and uncontentious sources of differences. Thus your belief is simply a statement of faith at this point, not evidence. Given all the previous failures it isn't clear why anyone would be wise to take your belief seriously *unless* you put it to such a test and showed you can do what you believe. Until then... To do this you would have to define what you mean by "most". i.e. do you mean more than half of all amps in use, or more than half the designs, or more than half of those ever used, etc? e.g. can we ignore the amps in TVs and portable radios and cheap 'music centers'? If so, we have to define the line that rules in/out a given amp, and give a plausible basis for doing so. Again, Serge guided me on this. This issue has been mentioned many times. 'Most' means virtually all modern SS amps that meet certain criteria (1). On such a basis the evidence supports what Serge has been saying. If you wish to contend with that you will need relevant assessable evidence for people to take you seriously. Given the history of this topic people will regard claims of what you are "pretty sure" of as no more than an unsupported belief of the kind which has in the past repeatedly been shown to have no foundation. I can only point out that "most" (indeed all) the relevant tests I know of showed no sign that those who listened could distinguish one amp from another - given a fairly basic set of requirements like level matching. I find this virtually impossible to do, even (or because of?) the crude sound meter I have. I assume the idea is to match levels between 20-20K Hz? You don't require a sound pressure meter if you are using the same speakers and listening position, etc, throughout. You can then use a meter to check the input voltages to the speakers and ensure they are about the same for one amp as for the other. If you find differences of the order of 1dB or more you can expect that to be audible. But if the differences are much smaller - e.g. around 0.1dB - then that is unlikely to produce an audible difference. Hence the aim is to make these as small as feasible, and well below 1dB. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html |
how good are class D amplifiers?
In article , Rob
wrote: Jim Lesurf wrote: Yes, that's right - 'distortion' is a concept, and not a thing. You point being that anything we observe in reality and then have a word for is a 'concept'? No, cheese is a thing, distortion is a concept. ....yet cheese is not milk. :-) I'm afraid that the problem here is with your understanding of the the topic, not in the topic (distortion) being discussed. Does that approach serve any purpose when we are trying to deal with reality? It seems to me to be no more than playing with words and doing this as a replacement for dealing with reality. In effect, a displacement acitivity. I'd rather dispense with the word distortion TBH. I'm afraid that it is defined and has a specific meaning. It means what we have been trying to explain to you. If you dislike this, then I'm afraid the problem is yours. Still, I'd (kind of) like to know why valves/vinyl sounds better. For techie types I think the term is 2nd harmonic distortion? Sweeping (and inaccurate) simplification, I'm afraid. First 'better' does not mean 'different'. Secondly, you are confusing a value judgement with a measurable and perceivable property/result (distortion) which can take many forms. Thirdly, 'valves' and 'vinyl' are gain devices and a form of polymer. Not a specific example of an amplifier, or a LP or a replay system. Finally, there are many sources of signal alterations in both LP systems and other, and in both SS and valve designs. So again I don't know who these 'techie types' are, but your statement looks to me like a string of vague and inaccurate terms. BTW If you want a totally different example of a way in which an LP may sound different to a CD keep yer eyes open for the issue of HFN that will appear cover-dated August 2007. 8-] Also have a look at the 'Clipping on CD' thread. :-) The point here is that any 'differences' may have little to do with 'valve' or 'vinyl' per se, but a great deal to do with how they may be used. It is perfectly reasonable for someone to decide to remain ignorant about some topic. There are many topics in which each of us have no interest. I tend to find interest in just about everything, except sport for some reason. However this means our views on such topics may be worthless. Or amusing (etc) - depends how they're put across. I've noticed that a lot of modern humour seems to be based on what IIRC an American described as 'shmo humour' (if I have spelled that correctly). The idea being that 'hilarious' things happen because the main character is a shmo or dimwit. Personally, I tend to find this type of 'comedy' uninteresting. I still think the 'amplifiers don't sound the same' hypothesis is interesting, worthwhile and (of course) grossly irritating round these parts. More 'boring' than 'irritating' I think. :-) At least that is my reaction to seeing the same claims and ideas I've seen countless times over the last 20-30 years. One reason is that the statement you make simply misrepresents the situation. Some do in some situations, others won't in others. Confusion between inherent and situation-dependent, etc, etc. Another is that such assertions aregenerally based on people never having done any appropriate forms of comparison test, being unaware of the many that have been done, and not really understanding the engineering, physics, etc, involved. People pop up on this group and elsewhere, make pretty much the same sweeping claims, ignore or dismiss the evidence we have, avoid the distinctions that can be made, then after a while go away without bothering to put their claims to a test. I've lost count of how often this happens. So if you wish to take this further, perhaps you should arrange to engage in a test of what you believe. run in a way that the rest of us can see the results and assess how the comparison was done. Otherwise is what you are saying anything other than a waste of time?... Is it 'conceptual' that when you build a bridge it does not collapse the next day? If you think so, then your meaning of the word differs from mine. I would also be reluctant to employ you to build bridges, or walk on/under any you designed. :-) And you'd be wise beyond your years :-) Considering how old I am, that would be remarkable. :-) FWIW The main reason I've spent decades studying, building, testing, etc, audio amplifiers and other kit is that I am largely driven by my enthusiasm for the results - being able to enjoy the music. My point, therefore, was that measurements, etc, are very valuable (if you understand them), and allow you to make more progress. And modesty no doubt forbids the qualification: 'measurement is not all' :-) No idea why you wrote that. You place great store in positivist data. Yet you consider the human response to that data as significant. 'Sounds rubbish' is not an example of positivist data. Not quite sure what the above means. :-) However FWIW my view of science tends to be based on the classic 'Popper' approach of testability and falsifiability. No idea how that relates to what you wrote. Measurement is not all - you know that, but didn't feel the need to say it. Actually I thought it was clear from what I said. :-) Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html |
how good are class D amplifiers?
Serge Auckland wrote:
"Rob" wrote in message [snip] (1) This was Serge's reply to my question 'what's necessary to ensure two amps sound the same': Here is my understanding of the threshold levels:- Distortions - all types, THD, IMD 0.1% Important Note: This distortion is measured from 20Hz to 20kHz with a bandwidth of 100kHz, and must be maesured into the loads declared suitable by the designer. For example, the QUAD 405 is rated at 100watts into any load 4-8 ohms. Consequently, I would expect it to work with loudspeakers rated at 6 ohms upwards. Note that 4 ohm rated loudspeakers can drop to 3.2 ohms, and would consequently fall outside QUAD's specification for the 405. Frequency response +-1dB 20Hz-20kHz Important note: This frequency response is measured across the loudspeaker load, *not* across a dummy load. This requires the amplifier to have a low output impdeance as otherwise, the loudspeaker's impedance characteristic will modify the frequency response. Hum and noise 80dB measured on a bandwidth of 20Hz-20kHz, and no worse than -60dB outside that band. It is important that the amplifier have no instabilities at sub or supersonic frequencies. Crosstalk: 60dB In practice, crosstalk below -40dB is unlikely to be audible under programme conditions. It is important that the distortion of the crosstalk be below 0.1% as otherwise, the crosstalk distortion could swamp the speaking channel's distortion. This is a rare condition, but not unknown with poor designs with poor power-supply rejection. Rob, Are you saying that even with two amplifiers meeting the above criteria you can hear a difference or that you can hear differences between amplifiers that may or may not meet the above criteria, you just don't know as you haven't made the measurements? I should make it clear that I've never made measurements, beyond crude level readings using a handheld 10UKP meter. My claim is a 'hunch' informed by listening, not hard data. If the former, then we should look into ths further, as it would be a valuable addition to our knowledge. If the latter, then of course, amplifiers with different performance characteristics can sound different. If any of the above criteria are not met, and the most obvious are level matching and frequency response differences, then in all probability they will sound different because they are. Level matching needs to be done carefully, and can only be valid if the frequency response of the two amplifiers is checked first, and found to be within +_1dB *of each other* into the loudspeaker load being used. I do of course realise that it would be useful (to say the least) to carry out some measurements. There are two sides to this: 1. Listening. The physical swapping out is doable. I would find/have found level matching incredibly difficult. I tried this some months ago with a 20-20k hz cd, taking levels at various points. I couldn't get close to level matching across the range - I'd got weird 'spikes' at points in the frequency range, around 2000hz IIRC. Even using the same amp! Anyway, this sort-of-obviously means I need some more reliable measuring equipment and techniques - any pointers here would be appreciated. 2. If listening using level matched DBT does reveal difference, the spotlight then turns on the amps. I would then have to measure the amps and see what variation there is. Again - a pointer would be useful - even a book. Once differences are identified and quantified, then any audible differences are soon accounted for. What I am saying is that with modern SS amplifiers, it is easy except at the very cheapest end for the above criteria to be met, consequently any but the cheapest amps will all sound the same when played at the same volume into the same (sensible) load. I experience four areas of difference - bass, 'soundstage', voices and 'top end'. Bass is easiest (A NAD 3020 was quite 'soft' compared to the clearly defined bass lines of a Rotel integrated), a Quad 405 is noticeably sibilant, and a Roksan Kandy I had a while ago was plain shrill. I'm using a Cambridge AV amp at the moment, and I can't detect a difference except at very high sound levels between its built in power amp, and a Rose power amp, and a Behringer power amp. I'm pretty pleased with the Cambridge for casual listening. The same applies to CD players and anything else that meets the criteria. Items that don't meet the criteria (rarely or never) are transducers and consequently microphones, pick-up cartridges and loudspeakers will all sound different for easily identified and measurable reasons. The *real* point I'd like to explore would be the notion that conventional measurements are not a reliable guide to sound experienced. Of course (again) such a statement comes across to some as something between witchcraft, homoeopathy and astrology, but I set it out here just so you can categorise my comments properly. Rob |
how good are class D amplifiers?
Arny Krueger wrote:
"Rob" wrote in message Others (on this NG, not you explicitly so far as I can tell) maintain this is highly unlikely. For example, I'm pretty sure I could hear the difference between a Cambridge audio power amp, a semi-pro power amp, and a Quad 405 power amp. Why would this even be of interest? I thought that audio is related to the love of music, not the peculiarities of amplifiers. I'll have to admit that, for me, audio does sometimes get in the way of a good tune for the wrong reasons. |
how good are class D amplifiers?
"Rob" wrote in message ... Serge Auckland wrote: "Rob" wrote in message [snip] (1) This was Serge's reply to my question 'what's necessary to ensure two amps sound the same': Here is my understanding of the threshold levels:- Distortions - all types, THD, IMD 0.1% Important Note: This distortion is measured from 20Hz to 20kHz with a bandwidth of 100kHz, and must be maesured into the loads declared suitable by the designer. For example, the QUAD 405 is rated at 100watts into any load 4-8 ohms. Consequently, I would expect it to work with loudspeakers rated at 6 ohms upwards. Note that 4 ohm rated loudspeakers can drop to 3.2 ohms, and would consequently fall outside QUAD's specification for the 405. Frequency response +-1dB 20Hz-20kHz Important note: This frequency response is measured across the loudspeaker load, *not* across a dummy load. This requires the amplifier to have a low output impdeance as otherwise, the loudspeaker's impedance characteristic will modify the frequency response. Hum and noise 80dB measured on a bandwidth of 20Hz-20kHz, and no worse than -60dB outside that band. It is important that the amplifier have no instabilities at sub or supersonic frequencies. Crosstalk: 60dB In practice, crosstalk below -40dB is unlikely to be audible under programme conditions. It is important that the distortion of the crosstalk be below 0.1% as otherwise, the crosstalk distortion could swamp the speaking channel's distortion. This is a rare condition, but not unknown with poor designs with poor power-supply rejection. Rob, Are you saying that even with two amplifiers meeting the above criteria you can hear a difference or that you can hear differences between amplifiers that may or may not meet the above criteria, you just don't know as you haven't made the measurements? I should make it clear that I've never made measurements, beyond crude level readings using a handheld 10UKP meter. My claim is a 'hunch' informed by listening, not hard data. If the former, then we should look into ths further, as it would be a valuable addition to our knowledge. If the latter, then of course, amplifiers with different performance characteristics can sound different. If any of the above criteria are not met, and the most obvious are level matching and frequency response differences, then in all probability they will sound different because they are. Level matching needs to be done carefully, and can only be valid if the frequency response of the two amplifiers is checked first, and found to be within +_1dB *of each other* into the loudspeaker load being used. I do of course realise that it would be useful (to say the least) to carry out some measurements. There are two sides to this: 1. Listening. The physical swapping out is doable. I would find/have found level matching incredibly difficult. I tried this some months ago with a 20-20k hz cd, taking levels at various points. I couldn't get close to level matching across the range - I'd got weird 'spikes' at points in the frequency range, around 2000hz IIRC. Even using the same amp! Anyway, this sort-of-obviously means I need some more reliable measuring equipment and techniques - any pointers here would be appreciated. This is quite normal:- If you are level-matching by using a SPL meter in-room, then what you are measuring is the sound pressure at the point at which you are holding the meter (so much is obvious :-) ) At mid-high frequencies, the measurement you make will be very influenced by local reflections, even from your own body. If I put my SPL meter on a photographic tripod, then move around even only by a few centimetres, the reading on the meter will vary by a dB or more at mid-high frequencies. At low frequencies, it is much more stable, being dependent on room reflections, and hence positioning in the room, much less influenced by body movements as the wavelength of the sound becomes larger than my body dimensions (even in my current less than sylph-like state) You should level-match by measuring across the 'speaker terminals ideally by using a high impedance audio millivoltmeter (once called a valve-voltmeter). I have found that my normal inexpensive multimeter is accurate enough at low audio frequencies. Mine actually work fine up to 20kHz, but if you use a 100Hz tone for level matching you should be fine. Use your SPL meter to make sure the volume level is around 85dBC (say 80dBA) at 100Hz and level-match with the multimeter at that loudness. You should fine it easy to level-match to better than 0.5dB even with a multimeter. 2. If listening using level matched DBT does reveal difference, the spotlight then turns on the amps. I would then have to measure the amps and see what variation there is. Again - a pointer would be useful - even a book. To make meaningful measurements on an amplifier you don't need a lot of test equipment, just a good soundcard that samples at 192kHz and some software. I prefer to use individual physical instruments, but that's because I'm both an old fart and happen to have them. If I wasn't the first and didn't have the second, then I would probably use the PC method totally. I have the RightMark audio analyser software which is freeware, and from what I can see works beatifully. http://audio.rightmark.org If you are going to make useful THD and frequency response measurements, you need a 192k sampling card to give you some 85 kHz of measuring bandwidth. You *will* need a good dummy load to run the amps into. I have four 50 watt 4 ohm resistors mounted on a large heatsink, each with a flying lead and croc clips. I can thus set up 4 x 4 ohms @ 50 watt, 2x8 ohms @ 100 watt, 2x 2 ohms @ 100 watt, 1x4 ohms @ 200 watt and other combinations. As for books, can't recommend anything specific, as my training was pretty much continuous since I was 16, in the days when a 100kHz 'scope was the best my school had. There are a number of good text books about, but they tend to be rather expensive. There's usually a bookshop at the pro-audio exhibitions, so if you get a chance to go to the AES, or IBC in Amsterdam or NAB in Las Vegas, or know anyone else going, they may be able to find one or two for you. Once differences are identified and quantified, then any audible differences are soon accounted for. What I am saying is that with modern SS amplifiers, it is easy except at the very cheapest end for the above criteria to be met, consequently any but the cheapest amps will all sound the same when played at the same volume into the same (sensible) load. I experience four areas of difference - bass, 'soundstage', voices and 'top end'. Bass is easiest (A NAD 3020 was quite 'soft' compared to the clearly defined bass lines of a Rotel integrated), a Quad 405 is noticeably sibilant, and a Roksan Kandy I had a while ago was plain shrill. I'm using a Cambridge AV amp at the moment, and I can't detect a difference except at very high sound levels between its built in power amp, and a Rose power amp, and a Behringer power amp. I'm pretty pleased with the Cambridge for casual listening. Just to give you some idea of how difficult it is to assess equipment subjectively, let me quote from the Hi-Fi Choice reviews for the NAD 3020/3120 and Quad 405:- NAD. "Bass showed a touch of boom while the mid seemed a little hard tonally and the treble was mildly grainy." Quad. " The treble was still showing some mild "feathery muzziness" while the bass could have offered more extension and impact." Both these amplifiers are flat to +- 1dB between 20Hz and 20kHz The same applies to CD players and anything else that meets the criteria. Items that don't meet the criteria (rarely or never) are transducers and consequently microphones, pick-up cartridges and loudspeakers will all sound different for easily identified and measurable reasons. The *real* point I'd like to explore would be the notion that conventional measurements are not a reliable guide to sound experienced. Of course (again) such a statement comes across to some as something between witchcraft, homoeopathy and astrology, but I set it out here just so you can categorise my comments properly. Rob Yes, witchcraft, homeopathy, astrology *and* subjective hi-fi reviewing are all characterised by believing things that do not show up under any sort of scientific scrutiny. Conventional measurements, *if applied correctly* can characterise completely the operation of a piece of audio equipment. What they can't do is to characterised your reaction to that piece of equipment. What I mean by this is that we all are conditioned by magazines, friends, received wisdom etc, and that we characterise the sound we hear according to our prejudices. When these prejudices are not able to operate, as in unsighted testing, then many of the previously-held views dissappear. So far, no-one has been able to come up with realiable evidence that there are some aspects of audio performance that we have not yet been able to measure. The closest I suppose is the performance of bit reduced digital encoders of the psychacoustic type. Conventional test measurements don't show up the artefacts we all claim to hear, although I have surprised myself as to just how good MPEG encoders are at low bit rates when listened to blind. When I was last working professionally with encoders, there was no standard test signal which would correlate with what we could hear, and as far as I can recall, every customer had a favourite CD or two which they used to evaluate audio quality. Possibly someone on this group may have more recent information on testing audio codecs. All other audio equipment is now so well understood and characterised by conventional measurements that when audio differences do show up, they are easily dealt with. Note however, that some products are deliberately designed to sound different, for marketing reasons. Linn realised this as long ago as the 80s with their Kan loudspeaker which was highly coloured and with an appalling frequency response. I can't believe that a company of Linn's engineering abilities did this by accident or incompetence, so it must have been deliberate to stand out in demos as sounding different to the rest of their competitors. More recently, popularity of SET amplifiers and high-efficiency horns points to the desire of listeners to have something that's different to the prevailing norm. S. http://audiopages.googlepages.com |
how good are class D amplifiers?
Serge Auckland wrote:
"Rob" wrote in message ... [snip to bit about measurement] 1. Listening. The physical swapping out is doable. I would find/have found level matching incredibly difficult. I tried this some months ago with a 20-20k hz cd, taking levels at various points. I couldn't get close to level matching across the range - I'd got weird 'spikes' at points in the frequency range, around 2000hz IIRC. Even using the same amp! Anyway, this sort-of-obviously means I need some more reliable measuring equipment and techniques - any pointers here would be appreciated. This is quite normal:- If you are level-matching by using a SPL meter in-room, then what you are measuring is the sound pressure at the point at which you are holding the meter (so much is obvious :-) ) At mid-high frequencies, the measurement you make will be very influenced by local reflections, even from your own body. If I put my SPL meter on a photographic tripod, then move around even only by a few centimetres, the reading on the meter will vary by a dB or more at mid-high frequencies. At low frequencies, it is much more stable, being dependent on room reflections, and hence positioning in the room, much less influenced by body movements as the wavelength of the sound becomes larger than my body dimensions (even in my current less than sylph-like state) Yes, I'd realised this - if not strictly taken it into account. Quite how I clamp the listener's head, and avoid ear twitching, is an issue for a later day :-) You should level-match by measuring across the 'speaker terminals ideally by using a high impedance audio millivoltmeter (once called a valve-voltmeter). I have found that my normal inexpensive multimeter is accurate enough at low audio frequencies. Mine actually work fine up to 20kHz, but if you use a 100Hz tone for level matching you should be fine. Use your SPL meter to make sure the volume level is around 85dBC (say 80dBA) at 100Hz and level-match with the multimeter at that loudness. You should fine it easy to level-match to better than 0.5dB even with a multimeter. Ak! I can't have that I'm afraid. I think I understand what you're saying, but what I'm saying is that loudspeakers are non-linear loads and something (I know not what) might be happening between the signal and the sound. I suppose my thinking here comes from tests of kit I've read in magazines, and the suggestion that different amplifiers do not do the 'wire with gain' thing in a linear way. But I'm afraid I can't remember the details - I don't even have a hifi magazine in the house, having given up on them many years ago. Now, if you're saying to me that any amplifier that has the specification you've detailed will interact with a given loudspeaker ('normal'/domestic) in exactly the same way within the specification you detailed then I'll do my best to satisfy myself that is in fact the case (if I can), and adopt your test. You just have to say 'it is the case' - I appreciate your patience thus far. In addition, I would expect the level matching to apply between 20 -20k hz - just my little quirk :-) 2. If listening using level matched DBT does reveal difference, the spotlight then turns on the amps. I would then have to measure the amps and see what variation there is. Again - a pointer would be useful - even a book. To make meaningful measurements on an amplifier you don't need a lot of test equipment, just a good soundcard that samples at 192kHz and some software. I prefer to use individual physical instruments, but that's because I'm both an old fart and happen to have them. If I wasn't the first and didn't have the second, then I would probably use the PC method totally. I have the RightMark audio analyser software which is freeware, and from what I can see works beatifully. http://audio.rightmark.org If you are going to make useful THD and frequency response measurements, you need a 192k sampling card to give you some 85 kHz of measuring bandwidth. You *will* need a good dummy load to run the amps into. I have four 50 watt 4 ohm resistors mounted on a large heatsink, each with a flying lead and croc clips. I can thus set up 4 x 4 ohms @ 50 watt, 2x8 ohms @ 100 watt, 2x 2 ohms @ 100 watt, 1x4 ohms @ 200 watt and other combinations. That's very interesting, thanks. I'm sure I have the bits and pieces to manage that, and it'd be a useful means of checking what I've got. As for books, can't recommend anything specific, as my training was pretty much continuous since I was 16, in the days when a 100kHz 'scope was the best my school had. There are a number of good text books about, but they tend to be rather expensive. There's usually a bookshop at the pro-audio exhibitions, so if you get a chance to go to the AES, or IBC in Amsterdam or NAB in Las Vegas, or know anyone else going, they may be able to find one or two for you. Thanks again. Really, this doesn't come easy to me. I tried reading a book on valve amplifier design - quite basic by all accounts. I got about a third of the way through and got stuck on one paragraph. I simply couldn't accept on face value what was said. I could make the effort one day (wilful ignorance,as Jim might say!), and post to one of the tech groups. I've never got stuck in the same way with some quite complicated political and social theory. And I would add that i have a day job ;-) Once differences are identified and quantified, then any audible differences are soon accounted for. What I am saying is that with modern SS amplifiers, it is easy except at the very cheapest end for the above criteria to be met, consequently any but the cheapest amps will all sound the same when played at the same volume into the same (sensible) load. I experience four areas of difference - bass, 'soundstage', voices and 'top end'. Bass is easiest (A NAD 3020 was quite 'soft' compared to the clearly defined bass lines of a Rotel integrated), a Quad 405 is noticeably sibilant, and a Roksan Kandy I had a while ago was plain shrill. I'm using a Cambridge AV amp at the moment, and I can't detect a difference except at very high sound levels between its built in power amp, and a Rose power amp, and a Behringer power amp. I'm pretty pleased with the Cambridge for casual listening. Just to give you some idea of how difficult it is to assess equipment subjectively, let me quote from the Hi-Fi Choice reviews for the NAD 3020/3120 and Quad 405:- NAD. "Bass showed a touch of boom while the mid seemed a little hard tonally and the treble was mildly grainy." Quad. " The treble was still showing some mild "feathery muzziness" while the bass could have offered more extension and impact." Both these amplifiers are flat to +- 1dB between 20Hz and 20kHz And I have to take into account I've probably read similar reviews, and they could affect what I'm hearing. I don't doubt that. The same applies to CD players and anything else that meets the criteria. Items that don't meet the criteria (rarely or never) are transducers and consequently microphones, pick-up cartridges and loudspeakers will all sound different for easily identified and measurable reasons. The *real* point I'd like to explore would be the notion that conventional measurements are not a reliable guide to sound experienced. Of course (again) such a statement comes across to some as something between witchcraft, homoeopathy and astrology, but I set it out here just so you can categorise my comments properly. Rob Yes, witchcraft, homeopathy, astrology *and* subjective hi-fi reviewing are all characterised by believing things that do not show up under any sort of scientific scrutiny. Conventional measurements, *if applied correctly* can characterise completely the operation of a piece of audio equipment. That they can is not in doubt. It's possible that some, on learning that they measure within limits, subsequently hear no difference. And some, on reading a review that is half-decent, hear difference. It's bothersome, I know. What they can't do is to characterised your reaction to that piece of equipment. What I mean by this is that we all are conditioned by magazines, friends, received wisdom etc, and that we characterise the sound we hear according to our prejudices. When these prejudices are not able to operate, as in unsighted testing, then many of the previously-held views dissappear. So far, no-one has been able to come up with realiable evidence that there are some aspects of audio performance that we have not yet been able to measure. The closest I suppose is the performance of bit reduced digital encoders of the psychacoustic type. Conventional test measurements don't show up the artefacts we all claim to hear, although I have surprised myself as to just how good MPEG encoders are at low bit rates when listened to blind. When I was last working professionally with encoders, there was no standard test signal which would correlate with what we could hear, and as far as I can recall, every customer had a favourite CD or two which they used to evaluate audio quality. Possibly someone on this group may have more recent information on testing audio codecs. I'm archiving about 300 CDs to disc before I get rid of them. I compared the wav rips to some 192kbs mp3s last night, and while I could hear a difference (just, I got caught out from time to time) it wasn't significant, and made *preference* very hard to establish. On a tangent, I am interested in learning why my valve amplifier sounds so good. Put simply, if all of this can be measured, why can't some sort of (distortion?!) filter be used to recreate the sound? The novelty of the glow has more or less worn off, and if such a thing existed I'd give it a go. All other audio equipment is now so well understood and characterised by conventional measurements that when audio differences do show up, they are easily dealt with. Note however, that some products are deliberately designed to sound different, for marketing reasons. Linn realised this as long ago as the 80s with their Kan loudspeaker which was highly coloured and with an appalling frequency response. I can't believe that a company of Linn's engineering abilities did this by accident or incompetence, so it must have been deliberate to stand out in demos as sounding different to the rest of their competitors. Speakers really are the sharp end of things IMO. My guess with Linn is that they had in mind a speaker that could (somehow) sound accurate (or their version of it) given domestic settings. I'm very happy with Dynaudio speakers, but I'm intrigued by Keith's various forays - impressive and disarming at once, and something I mean to try one day. More recently, popularity of SET amplifiers and high-efficiency horns points to the desire of listeners to have something that's different to the prevailing norm. Agreed - and in the scheme of things does no harm. http://audiopages.googlepages.com A good read, and a splendid system by the looks of it. A valve cartridge pre-amp wouldn't go amiss :-) Rob |
how good are class D amplifiers?
-- http://audiopages.googlepages.com "Rob" wrote in message ... Serge Auckland wrote: "Rob" wrote in message ... [snip to bit about measurement] 1. Listening. The physical swapping out is doable. I would find/have found level matching incredibly difficult. I tried this some months ago with a 20-20k hz cd, taking levels at various points. I couldn't get close to level matching across the range - I'd got weird 'spikes' at points in the frequency range, around 2000hz IIRC. Even using the same amp! Anyway, this sort-of-obviously means I need some more reliable measuring equipment and techniques - any pointers here would be appreciated. This is quite normal:- If you are level-matching by using a SPL meter in-room, then what you are measuring is the sound pressure at the point at which you are holding the meter (so much is obvious :-) ) At mid-high frequencies, the measurement you make will be very influenced by local reflections, even from your own body. If I put my SPL meter on a photographic tripod, then move around even only by a few centimetres, the reading on the meter will vary by a dB or more at mid-high frequencies. At low frequencies, it is much more stable, being dependent on room reflections, and hence positioning in the room, much less influenced by body movements as the wavelength of the sound becomes larger than my body dimensions (even in my current less than sylph-like state) Yes, I'd realised this - if not strictly taken it into account. Quite how I clamp the listener's head, and avoid ear twitching, is an issue for a later day :-) You should level-match by measuring across the 'speaker terminals ideally by using a high impedance audio millivoltmeter (once called a valve-voltmeter). I have found that my normal inexpensive multimeter is accurate enough at low audio frequencies. Mine actually work fine up to 20kHz, but if you use a 100Hz tone for level matching you should be fine. Use your SPL meter to make sure the volume level is around 85dBC (say 80dBA) at 100Hz and level-match with the multimeter at that loudness. You should fine it easy to level-match to better than 0.5dB even with a multimeter. Ak! I can't have that I'm afraid. I think I understand what you're saying, but what I'm saying is that loudspeakers are non-linear loads and something (I know not what) might be happening between the signal and the sound. I suppose my thinking here comes from tests of kit I've read in magazines, and the suggestion that different amplifiers do not do the 'wire with gain' thing in a linear way. But I'm afraid I can't remember the details - I don't even have a hifi magazine in the house, having given up on them many years ago. Loudspeakers are *not* in any way non-linear loads. The impedance of the 'speaker system varies with frequency, but (except for some electrostatics) there is no variation with level, consequently they *are* linear. Amplifiers are also linear to the limits of their distortion characteristics, which is why amplifiers need to have low distortion, maintained into the minimum load presented to them. What you may be referring to is that loudspeakers have impedances that drop well below (and raise well above) their nominal figure. Some amplifiers may change their sound at the impedance minima. This is true, but this is why I say that two amplifiers being compared have to be used within their design limits. If one amp is designed for 4-8 ohms, and another amp is designed for 3-8 ohms, then both should sound identical into a nominally 8 ohm 'speaker, but could well sound different into a nominally 4 ohm 'speaker as the minimum load could be 3.2 ohms (the minimum figure to qualify for a 4 ohm rating). Now, if you're saying to me that any amplifier that has the specification you've detailed will interact with a given loudspeaker ('normal'/domestic) in exactly the same way within the specification you detailed then I'll do my best to satisfy myself that is in fact the case (if I can), and adopt your test. You just have to say 'it is the case' - I appreciate your patience thus far. In addition, I would expect the level matching to apply between 20 -20k hz - just my little quirk :-) 2. If listening using level matched DBT does reveal difference, the spotlight then turns on the amps. I would then have to measure the amps and see what variation there is. Again - a pointer would be useful - even a book. To make meaningful measurements on an amplifier you don't need a lot of test equipment, just a good soundcard that samples at 192kHz and some software. I prefer to use individual physical instruments, but that's because I'm both an old fart and happen to have them. If I wasn't the first and didn't have the second, then I would probably use the PC method totally. I have the RightMark audio analyser software which is freeware, and from what I can see works beatifully. http://audio.rightmark.org If you are going to make useful THD and frequency response measurements, you need a 192k sampling card to give you some 85 kHz of measuring bandwidth. You *will* need a good dummy load to run the amps into. I have four 50 watt 4 ohm resistors mounted on a large heatsink, each with a flying lead and croc clips. I can thus set up 4 x 4 ohms @ 50 watt, 2x8 ohms @ 100 watt, 2x 2 ohms @ 100 watt, 1x4 ohms @ 200 watt and other combinations. That's very interesting, thanks. I'm sure I have the bits and pieces to manage that, and it'd be a useful means of checking what I've got. As for books, can't recommend anything specific, as my training was pretty much continuous since I was 16, in the days when a 100kHz 'scope was the best my school had. There are a number of good text books about, but they tend to be rather expensive. There's usually a bookshop at the pro-audio exhibitions, so if you get a chance to go to the AES, or IBC in Amsterdam or NAB in Las Vegas, or know anyone else going, they may be able to find one or two for you. Thanks again. Really, this doesn't come easy to me. I tried reading a book on valve amplifier design - quite basic by all accounts. I got about a third of the way through and got stuck on one paragraph. I simply couldn't accept on face value what was said. I could make the effort one day (wilful ignorance,as Jim might say!), and post to one of the tech groups. I've never got stuck in the same way with some quite complicated political and social theory. And I would add that i have a day job ;-) Once differences are identified and quantified, then any audible differences are soon accounted for. What I am saying is that with modern SS amplifiers, it is easy except at the very cheapest end for the above criteria to be met, consequently any but the cheapest amps will all sound the same when played at the same volume into the same (sensible) load. I experience four areas of difference - bass, 'soundstage', voices and 'top end'. Bass is easiest (A NAD 3020 was quite 'soft' compared to the clearly defined bass lines of a Rotel integrated), a Quad 405 is noticeably sibilant, and a Roksan Kandy I had a while ago was plain shrill. I'm using a Cambridge AV amp at the moment, and I can't detect a difference except at very high sound levels between its built in power amp, and a Rose power amp, and a Behringer power amp. I'm pretty pleased with the Cambridge for casual listening. Just to give you some idea of how difficult it is to assess equipment subjectively, let me quote from the Hi-Fi Choice reviews for the NAD 3020/3120 and Quad 405:- NAD. "Bass showed a touch of boom while the mid seemed a little hard tonally and the treble was mildly grainy." Quad. " The treble was still showing some mild "feathery muzziness" while the bass could have offered more extension and impact." Both these amplifiers are flat to +- 1dB between 20Hz and 20kHz And I have to take into account I've probably read similar reviews, and they could affect what I'm hearing. I don't doubt that. The same applies to CD players and anything else that meets the criteria. Items that don't meet the criteria (rarely or never) are transducers and consequently microphones, pick-up cartridges and loudspeakers will all sound different for easily identified and measurable reasons. The *real* point I'd like to explore would be the notion that conventional measurements are not a reliable guide to sound experienced. Of course (again) such a statement comes across to some as something between witchcraft, homoeopathy and astrology, but I set it out here just so you can categorise my comments properly. Rob Yes, witchcraft, homeopathy, astrology *and* subjective hi-fi reviewing are all characterised by believing things that do not show up under any sort of scientific scrutiny. Conventional measurements, *if applied correctly* can characterise completely the operation of a piece of audio equipment. That they can is not in doubt. It's possible that some, on learning that they measure within limits, subsequently hear no difference. And some, on reading a review that is half-decent, hear difference. It's bothersome, I know. What they can't do is to characterised your reaction to that piece of equipment. What I mean by this is that we all are conditioned by magazines, friends, received wisdom etc, and that we characterise the sound we hear according to our prejudices. When these prejudices are not able to operate, as in unsighted testing, then many of the previously-held views dissappear. So far, no-one has been able to come up with realiable evidence that there are some aspects of audio performance that we have not yet been able to measure. The closest I suppose is the performance of bit reduced digital encoders of the psychacoustic type. Conventional test measurements don't show up the artefacts we all claim to hear, although I have surprised myself as to just how good MPEG encoders are at low bit rates when listened to blind. When I was last working professionally with encoders, there was no standard test signal which would correlate with what we could hear, and as far as I can recall, every customer had a favourite CD or two which they used to evaluate audio quality. Possibly someone on this group may have more recent information on testing audio codecs. I'm archiving about 300 CDs to disc before I get rid of them. I compared the wav rips to some 192kbs mp3s last night, and while I could hear a difference (just, I got caught out from time to time) it wasn't significant, and made *preference* very hard to establish. On a tangent, I am interested in learning why my valve amplifier sounds so good. Put simply, if all of this can be measured, why can't some sort of (distortion?!) filter be used to recreate the sound? The novelty of the glow has more or less worn off, and if such a thing existed I'd give it a go. There are plenty of valve simulators available on the pro market for DAW plug-ins. They add level-dependent harmonic distortion, some low-level noise and soft clipping. Some people pass their mix or part of it through a reel-to-reel recorder to get a similar effect. All other audio equipment is now so well understood and characterised by conventional measurements that when audio differences do show up, they are easily dealt with. Note however, that some products are deliberately designed to sound different, for marketing reasons. Linn realised this as long ago as the 80s with their Kan loudspeaker which was highly coloured and with an appalling frequency response. I can't believe that a company of Linn's engineering abilities did this by accident or incompetence, so it must have been deliberate to stand out in demos as sounding different to the rest of their competitors. Speakers really are the sharp end of things IMO. My guess with Linn is that they had in mind a speaker that could (somehow) sound accurate (or their version of it) given domestic settings. I'm very happy with Dynaudio speakers, but I'm intrigued by Keith's various forays - impressive and disarming at once, and something I mean to try one day. I am perhaps a bit more cynical of Linn's motives, as the Kan wasn't in any sense of the word accurate. Dynamic, aggressive, punchy, loud, but not accurate...I also like Dynaudio 'speakers, found them very pleasant. Sort of 'speaker you don't tire of. More recently, popularity of SET amplifiers and high-efficiency horns points to the desire of listeners to have something that's different to the prevailing norm. Agreed - and in the scheme of things does no harm. http://audiopages.googlepages.com A good read, and a splendid system by the looks of it. A valve cartridge pre-amp wouldn't go amiss :-) Thanks. The two turntables both have built-in RIAA pre-amps, which are quiet and accurate in their EQ, so I have no real incentive to change. Valve preamps for MC cartridges have great overload figures, but tend to be a bit noisy, so I prefer SS. S. http://audiopages.googlepages.com |
how good are class D amplifiers?
Serge Auckland wrote:
-- http://audiopages.googlepages.com "Rob" wrote in message ... Serge Auckland wrote: "Rob" wrote in message ... [snip to bit about measurement] 1. Listening. The physical swapping out is doable. I would find/have found level matching incredibly difficult. I tried this some months ago with a 20-20k hz cd, taking levels at various points. I couldn't get close to level matching across the range - I'd got weird 'spikes' at points in the frequency range, around 2000hz IIRC. Even using the same amp! Anyway, this sort-of-obviously means I need some more reliable measuring equipment and techniques - any pointers here would be appreciated. This is quite normal:- If you are level-matching by using a SPL meter in-room, then what you are measuring is the sound pressure at the point at which you are holding the meter (so much is obvious :-) ) At mid-high frequencies, the measurement you make will be very influenced by local reflections, even from your own body. If I put my SPL meter on a photographic tripod, then move around even only by a few centimetres, the reading on the meter will vary by a dB or more at mid-high frequencies. At low frequencies, it is much more stable, being dependent on room reflections, and hence positioning in the room, much less influenced by body movements as the wavelength of the sound becomes larger than my body dimensions (even in my current less than sylph-like state) Yes, I'd realised this - if not strictly taken it into account. Quite how I clamp the listener's head, and avoid ear twitching, is an issue for a later day :-) You should level-match by measuring across the 'speaker terminals ideally by using a high impedance audio millivoltmeter (once called a valve-voltmeter). I have found that my normal inexpensive multimeter is accurate enough at low audio frequencies. Mine actually work fine up to 20kHz, but if you use a 100Hz tone for level matching you should be fine. Use your SPL meter to make sure the volume level is around 85dBC (say 80dBA) at 100Hz and level-match with the multimeter at that loudness. You should fine it easy to level-match to better than 0.5dB even with a multimeter. Ak! I can't have that I'm afraid. I think I understand what you're saying, but what I'm saying is that loudspeakers are non-linear loads and something (I know not what) might be happening between the signal and the sound. I suppose my thinking here comes from tests of kit I've read in magazines, and the suggestion that different amplifiers do not do the 'wire with gain' thing in a linear way. But I'm afraid I can't remember the details - I don't even have a hifi magazine in the house, having given up on them many years ago. Loudspeakers are *not* in any way non-linear loads. The impedance of the 'speaker system varies with frequency, but (except for some electrostatics) there is no variation with level, consequently they *are* linear. Amplifiers are also linear to the limits of their distortion characteristics, which is why amplifiers need to have low distortion, maintained into the minimum load presented to them. ***** That being the case, it's very likely that you're right - most modern amplifiers sound identical. I suspect we're at odds about the definition of linear, and variables under consideration, and hence the maintenance of linearity across all variables. It makes *sense* to me to measure the sound and not the voltage, but I think you're saying that has no sense - the two things come to the same in a linear way, and it's a waste of time measuring sound when there's a far easier method. What you may be referring to is that loudspeakers have impedances that drop well below (and raise well above) their nominal figure. Some amplifiers may change their sound at the impedance minima. This is true, but this is why I say that two amplifiers being compared have to be used within their design limits. If one amp is designed for 4-8 ohms, and another amp is designed for 3-8 ohms, then both should sound identical into a nominally 8 ohm 'speaker, but could well sound different into a nominally 4 ohm 'speaker as the minimum load could be 3.2 ohms (the minimum figure to qualify for a 4 ohm rating). ****** That's OK - I don't have any speakers below 3.5 ohms, and I'm pretty sure all the amps are OK to 4 ohms. And yes, I think that's where I get the non-linearity thing from, at least in part. Rob |
how good are class D amplifiers?
In article , Serge Auckland
wrote: "Rob" wrote in message ... 1. Listening. The physical swapping out is doable. I would find/have found level matching incredibly difficult. I tried this some months ago with a 20-20k hz cd, taking levels at various points. I couldn't get close to level matching across the range - I'd got weird 'spikes' at points in the frequency range, around 2000hz IIRC. Even using the same amp! Anyway, this sort-of-obviously means I need some more reliable measuring equipment and techniques - any pointers here would be appreciated. This is quite normal:- If you are level-matching by using a SPL meter in-room, then what you are measuring is the sound pressure at the point at which you are holding the meter (so much is obvious :-) ) At mid-high frequencies, the measurement you make will be very influenced by local reflections, even from your own body. This is another reason why 'casual' listening tests can be so unreliable. Small changes of the listening position, etc, can affect the sound reaching the ears. Thus this is one of many factors which can produce 'differences' even if the amplifiers are functionally identical. You *will* need a good dummy load to run the amps into. I have four 50 watt 4 ohm resistors mounted on a large heatsink, each with a flying lead and croc clips. I can thus set up 4 x 4 ohms @ 50 watt, 2x8 ohms @ 100 watt, 2x 2 ohms @ 100 watt, 1x4 ohms @ 200 watt and other combinations. If you can stand the 'noise' it can also be revealing to do some measurements using the speakers as loads. This may expose effects that don't show up with resistive loads. However as well as the row, this can risk speaker damage unless you take care. As for books, can't recommend anything specific, as my training was pretty much continuous since I was 16, in the days when a 100kHz 'scope was the best my school had. There are a number of good text books about, but they tend to be rather expensive. There's usually a bookshop at the pro-audio exhibitions, so if you get a chance to go to the AES, or IBC in Amsterdam or NAB in Las Vegas, or know anyone else going, they may be able to find one or two for you. I can't off-hand think of a book suitable for 'beginners' that explains how they can do a sensible set of tests on something like an amplifier. Can anyone suggest one? I'd agree that these days what would be 'best' would probably be one that allows the user to make use of their computer with an audio input as the test instrument, and to use a test CD as the source. FWIW I've recently been writing a series of short articles for a computing mag which deals with how people can generate and analyse sound files. It would be useful to know if there is a decent book dealing with amp testing, or indeed testing other items of audio gear, which would be suitable for enthusuasts who don't already have experience and know how such things are done, and why. Just to give you some idea of how difficult it is to assess equipment subjectively, let me quote from the Hi-Fi Choice reviews for the NAD 3020/3120 and Quad 405:- NAD. "Bass showed a touch of boom while the mid seemed a little hard tonally and the treble was mildly grainy." Quad. " The treble was still showing some mild "feathery muzziness" while the bass could have offered more extension and impact." Both these amplifiers are flat to +- 1dB between 20Hz and 20kHz The problem with such statements in 'reviews' is that we not only have no idea if they were based on a genuine difference. We also can't tell if they were due to something like the reviewer moving their head an inch, or opening the room door, or... A number of controlled tests have been done where the amps A and B were played in randomised pairings. i.e. in each case A was played then A, or A then B, or B then B, or B then A. The listeners were asked in each case if the sound for each example in a pair was the 'same' or 'different'. This exposed a significant (statistically) tendency for people to say that AA or BB were 'different' rather than 'same'. Thus showing that people report differences when the amp is unchanged and the system has not been altered. Yes, witchcraft, homeopathy, astrology *and* subjective hi-fi reviewing are all characterised by believing things that do not show up under any sort of scientific scrutiny. That is perhaps a little unfair as some reports may well be reliable. The snag is distinguishing them from the unreliable claims. Alas, if you have no way of telling if an individual claim is reliable or not, and the authors are well-known for making claims which can't be backed up, then their claims become worthless. Might as well toss coins to make a decision as to use the reviews as a basis. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html |
how good are class D amplifiers?
In article , Rob
wrote: Serge Auckland wrote: "Rob" wrote in message ... [snip to bit about measurement] Yes, I'd realised this - if not strictly taken it into account. Quite how I clamp the listener's head, and avoid ear twitching, is an issue for a later day :-) You don't need to do that. Indeed it would be futile as there will be other variables which will be likely to change in an unpredictable way and which you won't be monitoring. The appropriate response is to make *many* tests and allow your head to move as you please in each case. This will tend over time to average away the effect of the uncontrolled variable and systematic effects then show through the statistical analysis. Of course, if the uncontrolled/unknown variables are so pervasive and serious, then it may be daft to waste time trying to see if you can find any amplifier 'differences' which they have swamped. Indeed, this is often my experience, and has for years seemed to me to make following this topic beyond a given point rather a waste of time. However if others wish to struggle to find evidence for amp 'differences' which seem to vanish in simply comparison tests I guess I should just allow them to waste their own time. If they ever find anything I'd be interested. :-) You should level-match by measuring across the 'speaker terminals ideally by using a high impedance audio millivoltmeter (once called a valve-voltmeter). I have found that my normal inexpensive multimeter is accurate enough at low audio frequencies. Mine actually work fine up to 20kHz, but if you use a 100Hz tone for level matching you should be fine. Use your SPL meter to make sure the volume level is around 85dBC (say 80dBA) at 100Hz and level-match with the multimeter at that loudness. You should fine it easy to level-match to better than 0.5dB even with a multimeter. Ak! I can't have that I'm afraid. I think I understand what you're saying, but what I'm saying is that loudspeakers are non-linear loads and something (I know not what) might be happening between the signal and the sound. Unfortunately vague feelings you have that something might be happening, but you've no idea what/how/why/etc are in themselves worthless. The requirement is quite simple in principle. You form an idea as to a 'cause' and then devise a test for it, then do the test and evaluate the evidence. The snag is that a suitable test requires some knowledge and understanding to devise. And that then doing the test and evaluating the results requires more understanding and some sweat. The cost of mining understanding from a flood of formless fears and delusions, I'm afraid. I suppose my thinking here comes from tests of kit I've read in magazines, and the suggestion that different amplifiers do not do the 'wire with gain' thing in a linear way. But I'm afraid I can't remember the details - I don't even have a hifi magazine in the house, having given up on them many years ago. Now, if you're saying to me that any amplifier that has the specification you've detailed will interact with a given loudspeaker ('normal'/domestic) in exactly the same way within the specification you detailed then I'll do my best to satisfy myself that is in fact the case (if I can), and adopt your test. You just have to say 'it is the case' - I appreciate your patience thus far. In addition, I would expect the level matching to apply between 20 -20k hz - just my little quirk :-) The key point is that the loudspeaker has specifically limited info on what amplifer you are using. It can't read the name badge, nor the reviews. It can't look and see if you have valves or transistors. It just finds that a pattern of voltages is being asserted on its input terminals. If two amplifiers are able to assert the same pattern and level of voltage, they will be able to supply the same current and power patterns. Either the speaker then delivers the same results in both cases or it does not. If it does not, then any 'difference' is due to the speakers, not the amp. If it does, then the amps are functionally the same so far as the test system is concerned. Thanks again. Really, this doesn't come easy to me. I tried reading a book on valve amplifier design - quite basic by all accounts. I got about a third of the way through and got stuck on one paragraph. I simply couldn't accept on face value what was said. I could make the effort one day (wilful ignorance,as Jim might say!), and post to one of the tech groups. I've never got stuck in the same way with some quite complicated political and social theory. And I would add that i have a day job ;-) It is not 'wilful ignorance' if you are trying as and when you can, despite finding it hard going (or inconvenient). These matters are *not* either trivial or self-evident. People have spent many hard years working on them to develop an understanding. The 'wilful ignorance' is when people can't be bothered to study and understand what has been done and airly dismiss any evidence-based results which do not suit their personal fancies. Just to give you some idea of how difficult it is to assess equipment subjectively, let me quote from the Hi-Fi Choice reviews for the NAD 3020/3120 and Quad 405:- NAD. "Bass showed a touch of boom while the mid seemed a little hard tonally and the treble was mildly grainy." Quad. " The treble was still showing some mild "feathery muzziness" while the bass could have offered more extension and impact." Both these amplifiers are flat to +- 1dB between 20Hz and 20kHz And I have to take into account I've probably read similar reviews, and they could affect what I'm hearing. I don't doubt that. Please bear in mind that a great deal of what appears in magazine reviews may well be tosh. This can apply to the 'measured results' in some cases as well as the impressive purple prose about the 'sound'. Treat with great caution. I'm archiving about 300 CDs to disc before I get rid of them. I compared the wav rips to some 192kbs mp3s last night, and while I could hear a difference (just, I got caught out from time to time) it wasn't significant, and made *preference* very hard to establish. Erm... what will you do when the HD fails without warning? On a tangent, I am interested in learning why my valve amplifier sounds so good. Put simply, if all of this can be measured, why can't some sort of (distortion?!) filter be used to recreate the sound? The novelty of the glow has more or less worn off, and if such a thing existed I'd give it a go. 1) Don't assume any difference is for the reason you give. :-) 2) Look carefully at reviews of valve amps. Note when you can what they say about 'output impedance' or 'damping factor'. 3) Note than many reviews and makers specs simply fail to mention various factors which may well affect the results - particularly with the common types of valve amp design. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html |
how good are class D amplifiers?
In article , Serge Auckland
wrote: You put everything into the 'sig' of the posting so I had to fiddle about the rescue it for the following: Ak! I can't have that I'm afraid. I think I understand what you're saying, but what I'm saying is that loudspeakers are non-linear loads and something Loudspeakers are *not* in any way non-linear loads. Erm... IIUC that isn't correct. 'Dynamic' (i.e. coil and magnet) speakers have distinct nonlinearities. e.g. the inductance of the coil is affected by its surroundings and the interaction varies with displacement. I have a feeling there are JAES papers on this stemming from ideas about changing from voltage drive to current drive. IIRC There is also a similar effect in terms of the back EMF varying with the changing field coupling. I think this can be measured as current waveform effects. However that does not change the basis of using the voltage input to the speaker for setting levels when doing an amp comparison as any speaker nonlinearity will be 'common mode'. If you are using the same speaker to compare two amps, either they are (un)affected by the above in the (audibly) same way, or not. On a tangent, I am interested in learning why my valve amplifier sounds so good. Put simply, if all of this can be measured, why can't some sort of (distortion?!) filter be used to recreate the sound? The novelty of the glow has more or less worn off, and if such a thing existed I'd give it a go. There are plenty of valve simulators available on the pro market for DAW plug-ins. They add level-dependent harmonic distortion, some low-level noise and soft clipping. Some people pass their mix or part of it through a reel-to-reel recorder to get a similar effect. That does. however, omit the frequency response changes which arise when a valve amp design has a high output impedance and the speaker has a load impedance that varies a lot with frequency. Some recent reviews I've seen list 'samping factors' down to about 2! I'd be amazed if that didn't change the results quite audibly with many speakers. Indeed, it seemed to me to make a subjective review worthless unless you are going to use the same speakers as the reviewer. (Alas, they sometimes don't bother to say what speakers they used, which doesn't help much!) The above point are examples of why I've personally always been a fan of people taking o/p impedance measurements more seriously than is normal in audio mags. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html |
how good are class D amplifiers?
Jim Lesurf wrote:
In article , Rob wrote: Jim Lesurf wrote: Is your concern simply that the evidence is based only on all the cases tried? If so, it is open to you or anyone else to collect more evidence. i.e. to carry out more comparison tests of appropriate kinds. My concern (such as it is) is simply this: I maintain different modern SS amplifiers can sound different. It is essentially self-evident that they 'can'. Indeed, you can choose to design two amps so that they do. However when people have done tests on amps that were not specifically designed to do this and which were designed to amplify, then they tend to be able to distinguishg one from another. i.e. they are found not to 'sound different'. But if you choose a design which is - either by deliberate choice or incompetence - making the output sufficiently different from a scaled version of the input then it may well 'sound different'. I wouldn't mean to use or buy an incompetent amplifier. I take it you'd consider anything from the big names (Sony, Cambridge, Rotel, NAD, Quad, Behringer etc) to be competent - in the sense that if they did turn out to be incompetent you'd be surprised. They are particularly affected by load (speakers) in my extraordinarily humble opinion. Others (on this NG, not you explicitly so far as I can tell) maintain this is highly unlikely. For example, I'm pretty sure I could hear the difference between a Cambridge audio power amp, a semi-pro power amp, and a Quad 405 power amp. Well you may be "pretty sure", but the problem is that many people in the past have been "pretty sure" of similar claims - but then failed to be able to do what they were "pretty sure" of when tested on the basis of the sounds in a matter that excluded well known and uncontentious sources of differences. Thus your belief is simply a statement of faith at this point, not evidence. Given all the previous failures it isn't clear why anyone would be wise to take your belief seriously *unless* you put it to such a test and showed you can do what you believe. Until then... Well, it's the result of experience. Many people claim similar experiences. As 'evidence' of 'fact' I'd agree that it's flimsy. Faith? Belief with reason? Yes, we agree. I don't think there's much point going over this again. You may not (hopefully!) remember, but this comes up every six months or so. I'm simply trying to get across that it's a hypothesis worth testing, and Serge has kindly offered some practical tips to test the notion. The problem I have is that technocrats *seem* on occasion rather condescending towards the opinions of others, without offering a reasoned explanation for their experience. Perhaps if I explain it this way - it's not what people think and say, but why they think and say it, which is of most importance. Do you *know* (or even have the vaguest idea) why people (like me) experience these 'physical world anomalies'? I certainly don't *know*. To do this you would have to define what you mean by "most". i.e. do you mean more than half of all amps in use, or more than half the designs, or more than half of those ever used, etc? e.g. can we ignore the amps in TVs and portable radios and cheap 'music centers'? If so, we have to define the line that rules in/out a given amp, and give a plausible basis for doing so. Again, Serge guided me on this. This issue has been mentioned many times. 'Most' means virtually all modern SS amps that meet certain criteria (1). On such a basis the evidence supports what Serge has been saying. If you wish to contend with that you will need relevant assessable evidence for people to take you seriously. Given the history of this topic people will regard claims of what you are "pretty sure" of as no more than an unsupported belief of the kind which has in the past repeatedly been shown to have no foundation. Again, we've trawled through all of this. It *is* supported, albeit not with the scientific test *you* require. I can only point out that "most" (indeed all) the relevant tests I know of showed no sign that those who listened could distinguish one amp from another - given a fairly basic set of requirements like level matching. I find this virtually impossible to do, even (or because of?) the crude sound meter I have. I assume the idea is to match levels between 20-20K Hz? You don't require a sound pressure meter if you are using the same speakers and listening position, etc, throughout. You can then use a meter to check the input voltages to the speakers and ensure they are about the same for one amp as for the other. If you find differences of the order of 1dB or more you can expect that to be audible. But if the differences are much smaller - e.g. around 0.1dB - then that is unlikely to produce an audible difference. Hence the aim is to make these as small as feasible, and well below 1dB. Yes, thanks, Serge helped me on that one as well. Rob |
how good are class D amplifiers?
"Rob" wrote in message
I don't think there's much point going over this again. Agreed, but that doesn't seem to stop you, Rob. You may not (hopefully!) remember, but this comes up every six months or so. It is so trite... I'm simply trying to get across that it's a hypothesis worth testing, It is a hyposthesis that at this point has been tested to death. The results are well-known among those who have done a craftsmanlike job of testing it. If you can competently search the web, the resources and evidence are all there. |
how good are class D amplifiers?
In article , Rob
wrote: Jim Lesurf wrote: In article , Rob wrote: Jim Lesurf wrote: My concern (such as it is) is simply this: I maintain different modern SS amplifiers can sound different. It is essentially self-evident that they 'can'. Indeed, you can choose to design two amps so that they do. However when people have done tests on amps that were not specifically designed to do this and which were designed to amplify, then they tend to be able to distinguishg one from another. i.e. they are found not to 'sound different'. But if you choose a design which is - either by deliberate choice or incompetence - making the output sufficiently different from a scaled version of the input then it may well 'sound different'. I wouldn't mean to use or buy an incompetent amplifier. I take it you'd consider anything from the big names (Sony, Cambridge, Rotel, NAD, Quad, Behringer etc) to be competent - in the sense that if they did turn out to be incompetent you'd be surprised. Actually, I have long ceased being 'surprised' by what makers do at times. :-) Hence I'd wary of placing too much reliance on the name badge. Particularly now that various brands are no longer owned by the original people who built them up to have a reputation for quality. e.g. Despite Sony being a regarded name I recently tried a DVD recorder from them. It had a cooling fan that was so loud that it was distracting when listening to dialogue on items recorded. This is absurd and needless, yet when I asked a local Sony center their reaction was 'they all do it'. They seemed not to think it was a problem, and clearly had no idea that quiet fans can be bought. Perhaps they think everyone is too busy looking at the pictures to notice the sound of a helicopter accompanying it. ;- The above is nothing to do with amps per se. But it shows that some companies end up being run by suits, and have development engineers who just produce what they are told by the suits and go home with their paychecks. The spec says nothing about the fan not making a loud noise, so this cheap one is fine... I've also repeatedly witnessed companies who bring out 'new' products distinctly worse than the ones they'd made a year or two before. Different suits and a different R&D team. No internal communications. No clue. The relevant suits and engineers are often isolated from the public and getting contact with them is almost impossible in practice. [snip] Well you may be "pretty sure", but the problem is that many people in the past have been "pretty sure" of similar claims - but then failed to be able to do what they were "pretty sure" of when tested on the basis of the sounds in a matter that excluded well known and uncontentious sources of differences. Thus your belief is simply a statement of faith at this point, not evidence. Given all the previous failures it isn't clear why anyone would be wise to take your belief seriously *unless* you put it to such a test and showed you can do what you believe. Until then... Well, it's the result of experience. Many people claim similar experiences. As 'evidence' of 'fact' I'd agree that it's flimsy. Faith? Belief with reason? Yes, we agree. Many people claim many things - often contradicting one another in the process. People believe all kinds of things. And tests in this area have often shown that what someone believes they can do, they are unable to show they could do when tested. To the point where many reviewers decided to stop participating in such tests and instead behave as if they'd never happened. There are simply too many ways for someone to decide that a 'difference' they hear is for one reason when in reality it is for another that hasn't occurred to them, or they have made a simple mistake. Hence 'evidence' comes from tests which are designed to deal with these problems and produce results whose reliability and relevance can be assessed by others who understand the problems. This means people can decide on the basis of the evidence returned, and avoids having to accept what they are told in a claim which may be worthless nonsense. Perhaps if I explain it this way - it's not what people think and say, but why they think and say it, which is of most importance. Do you *know* (or even have the vaguest idea) why people (like me) experience these 'physical world anomalies'? I certainly don't *know*. What we (i.e. various engineers and experimental scientists who have studied these topics seriously and engaged in tests, etc) 'know' (from both experience and study) is that there are many pitfalls and other effects that can cause people to ascribe the wrong 'reason' to what they think they heard. Thus claims by people who don't know and understand the 'history' of this topic nor the science tend to be greeted with sighs and groans. This is why some of the reactions you get are dismissive or sharp. It is a loop some of us have been round countless times for decades. I get involved partly to try and point out to people that there is a great deal on these topics which has aready been covered, and that the problems of claims are also not new. Partly because I am open to the idea that every now and then someone will come up with a genuinely 'new' idea or discovery. Alas, this openness seems not to pan out in general... it does mean I get bored at times at seeing the same old claims with the same lack of a reliable basis or understanding by the claimant of the problems. None of the above means 'all amps sound the same'. Nor that 'they all sound different'. But it does means that claims which are not based on taking the above into account are generally worthless. I can take an interest in discussing them here as I do so for the reasons I give. But most professionals in, say, the AES or IEEE would regard discussions on this topic as a waste of breath, and expose you to abuse from people who can't bear the idea that what they claim may simply be wrong. Look back a few decades and you can find out why... Again, Serge guided me on this. This issue has been mentioned many times. 'Most' means virtually all modern SS amps that meet certain criteria (1). On such a basis the evidence supports what Serge has been saying. If you wish to contend with that you will need relevant assessable evidence for people to take you seriously. Given the history of this topic people will regard claims of what you are "pretty sure" of as no more than an unsupported belief of the kind which has in the past repeatedly been shown to have no foundation. Again, we've trawled through all of this. It *is* supported, albeit not with the scientific test *you* require. Afraid not. 'Support' does not mean that 'many people have the same opinion'. Afraid you are still thinking in 'social science' terms, not those of science and engineering. Nor does 'support' mean a result which may be for many other well-established reasons which were ignored by the claimant. Distinction between an observation and claiming the *reason* for it. Someone may hear a 'difference' when they changed one amp for another - but that does not support the amps being the *reason* *unless* the other factors which can cause a change are dealt with. Your approach would mean all views are 'supported' which makes 'support' worthless since the 'supported' views conflict. Thus the need for boringly tedious things like an appropriate test method to deal with the various types of factors which otherwise cause misleading results, and to produce assessable evidence rather than bald statements of 'faith'. What matters is support by reliable, assessable, *evidence*. (This means both the test method and the results.) I am not talking about one single form of 'scientific test'. I am talking about the approach being relevant and able to be shown to be capable of producing reliable results rather than simple, well known, errors. I am also talking about people knowing about, and understanding, the many tests and sets of evidence which already exist and have largely settled these matters for most professional engineers and academic scientists. The point is that there are many well-known pitfalls and factors which can produce 'differences' which have nothing to do with changing one amp for another. Unless a comparison deals with these a claim that a change was due to one *amp* 'sounding different' to another is worthless. It also is a waste of time given that the pitfalls, and ways to deal with them, are well known to those who have studied the topic seriously. Given this it is perhaps understandable when some become irritable at seeing repeated claims based on ignorance or dismissal of these factors. It is also why I've come to expect evidence rather that assertions of faith or confidence. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html |
how good are class D amplifiers?
"Jim Lesurf" wrote in message ... In article , Serge Auckland wrote: You put everything into the 'sig' of the posting so I had to fiddle about the rescue it for the following: Ak! I can't have that I'm afraid. I think I understand what you're saying, but what I'm saying is that loudspeakers are non-linear loads and something Loudspeakers are *not* in any way non-linear loads. Erm... IIUC that isn't correct. 'Dynamic' (i.e. coil and magnet) speakers have distinct nonlinearities. e.g. the inductance of the coil is affected by its surroundings and the interaction varies with displacement. I have a feeling there are JAES papers on this stemming from ideas about changing from voltage drive to current drive. IIRC There is also a similar effect in terms of the back EMF varying with the changing field coupling. I think this can be measured as current waveform effects. However that does not change the basis of using the voltage input to the speaker for setting levels when doing an amp comparison as any speaker nonlinearity will be 'common mode'. If you are using the same speaker to compare two amps, either they are (un)affected by the above in the (audibly) same way, or not. Jim, as befits an academic, is of course correct in saying that there are non-linearities, but as far as I know these are secondary if not tertiary effects which are swamped by the mechanical non-linearities of a loudspeaker. The variation in load impedance with displacement is of such a low level that, in engineering terms if not in academic terms, can be safely ignored. Jim, if you have some figures that are at odds with this view, I would be interested to know them. S. -- http://audiopages.googlepages.com |
how good are class D amplifiers?
"Serge Auckland" wrote in
message "Jim Lesurf" wrote in message ... In article , Serge Auckland wrote: You put everything into the 'sig' of the posting so I had to fiddle about the rescue it for the following: Ak! I can't have that I'm afraid. I think I understand what you're saying, but what I'm saying is that loudspeakers are non-linear loads and something Loudspeakers are *not* in any way non-linear loads. Erm... IIUC that isn't correct. 'Dynamic' (i.e. coil and magnet) speakers have distinct nonlinearities. e.g. the inductance of the coil is affected by its surroundings and the interaction varies with displacement. I have a feeling there are JAES papers on this stemming from ideas about changing from voltage drive to current drive. IIRC There is also a similar effect in terms of the back EMF varying with the changing field coupling. I think this can be measured as current waveform effects. This is measureable, but generally slight. However that does not change the basis of using the voltage input to the speaker for setting levels when doing an amp comparison as any speaker nonlinearity will be 'common mode'. If you are using the same speaker to compare two amps, either they are (un)affected by the above in the (audibly) same way, or not. Agreed. When we did ABX tests of amplifiers, we set voltage levels measured across the speaker's input terminals. We *never* noticed any effects due to speaker nonlinearity. However, our measurements were within 0.1 dB which is about 1%. That means that there might have been nonlinear effects below 1% that we did not measure. However, if there were audible effects, they would have been heard in our ABX tests. Jim, as befits an academic, is of course correct in saying that there are non-linearities, but as far as I know these are secondary if not tertiary effects which are swamped by the mechanical non-linearities of a loudspeaker. That can be true from the acoustical side. These sorts of things are most important at low frequencies. In the middle range, they tend to be far smaller. At low frequencies they tend to be masked by the natural acoustical nonlinearity of the speaker. The variation in load impedance with displacement is of such a low level that, in engineering terms if not in academic terms, can be safely ignored. Jim, if you have some figures that are at odds with this view, I would be interested to know them. It's usually a second or third order effect under normal listening conditions. |
how good are class D amplifiers?
"Rob" wrote in message
The *real* point I'd like to explore would be the notion that conventional measurements are not a reliable guide to sound experienced. Investigations of this kind ahve been made by people with far better resources than you seem to have available to you. Of course (again) such a statement comes across to some as something between witchcraft, homoeopathy and astrology, but I set it out here just so you can categorise my comments properly. There's nothing wrong with wondering whether or not a full set of conventional measurements are a reliable guide to sound quality in normal listening. It is a question that has been answered again and again, affirming the idea that a full set of conventional measurements are a reliable guide to sound quality. |
how good are class D amplifiers?
In article , Serge Auckland
wrote: "Jim Lesurf" wrote in message ... In article , Serge Auckland wrote: Loudspeakers are *not* in any way non-linear loads. Erm... IIUC that isn't correct. 'Dynamic' (i.e. coil and magnet) speakers have distinct nonlinearities. e.g. the inductance of the coil is affected by its surroundings and the interaction varies with displacement. I have a feeling there are JAES papers on this stemming from ideas about changing from voltage drive to current drive. IIRC There is also a similar effect in terms of the back EMF varying with the changing field coupling. I think this can be measured as current waveform effects. However that does not change the basis of using the voltage input to the speaker for setting levels when doing an amp comparison as any speaker nonlinearity will be 'common mode'. If you are using the same speaker to compare two amps, either they are (un)affected by the above in the (audibly) same way, or not. Jim, as befits an academic, is of course correct in saying that there are non-linearities, but as far as I know these are secondary if not tertiary effects which are swamped by the mechanical non-linearities of a loudspeaker. I'm not sure of the 'secondary'/'tertiary' point. However I'd agree that the transducer nonlinearities seem to be dominant. The variation in load impedance with displacement is of such a low level that, in engineering terms if not in academic terms, can be safely ignored. Yes. It is certainly the case that people tend to ignore the impedance nonlinearities for quite sensible practical reasons. One being as you give. Another reason IIRC is because the general expectation is that the amp will have a low output impedance and the speaker works on the basis of translating the asserted voltage patterns into sound pressure ones. That implies that the load nonlinearity only matters to the poor amp maker who has to ensure the appropiate current is delivered 'on demand' by the load. :-) Jim, if you have some figures that are at odds with this view, I would be interested to know them. I don't have any figures in mind, and agree with what you say. IIRC there is at least one AES paper that looked at this and decided the effects were (on the above basis) not worth too much concern, but I can't recall details. I think the area cropped up due to muddles about the claimed effects of 'bi wiring' wrt speaker distortion, but I'd need to check that. These areas have been riddled with confused claims and attempts by others to sort the reality from the nonsense. However I have more recently become curious about combinations of speaker load nonlinearity and amplifiers which have relatively high output impedances which may also vary with frequency and signal level. Where the assumptions that seem reasonable and sensible to most audio engineers may not hold. One of the topics on my 'to do' list to look at sometime... :-) Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html |
how good are class D amplifiers?
In article , Arny
Krueger wrote: There's nothing wrong with wondering whether or not a full set of conventional measurements are a reliable guide to sound quality in normal listening. It is a question that has been answered again and again, affirming the idea that a full set of conventional measurements are a reliable guide to sound quality. Alas, the problem seems to be that many 'reviews' not only fail to make appropriate measurements. They also fail to give any explanation of their meanings and what can be drawn from them. Instead the 'review' has purple prose extolling the writer's impressions about a system and room the readers will never use. Slainte, Jim -- Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html |
how good are class D amplifiers?
"Arny Krueger" wrote There's nothing wrong with wondering whether or not a full set of conventional measurements are a reliable guide to sound quality in normal listening. It is a question that has been answered again and again, affirming the idea that a full set of conventional measurements are a reliable guide to sound quality. So simple, isn't it? When you are selecting kit, you just buy a heap of stuff where the figures (or, at least, the figures 'as claimed') tell you it'll work and Bob's your uncle! Yet the (hifi) world is full of people who have done just that and who are not happy with the result - time and time again, some of 'em! You'd think it would be impossible to get it wrong, wouldn't you?? |
how good are class D amplifiers?
"Jim Lesurf" wrote e.g. Despite Sony being a regarded name I recently tried a DVD recorder from them. It had a cooling fan that was so loud that it was distracting when listening to dialogue on items recorded. This is absurd and needless, yet when I asked a local Sony center their reaction was 'they all do it'. They seemed not to think it was a problem, and clearly had no idea that quiet fans can be bought. Perhaps they think everyone is too busy looking at the pictures to notice the sound of a helicopter accompanying it. ;- Given your supersensitivity to noise ('rifle shots' on vinyl for example) I can see it would be a problem, but the harsh reality is that even SS/digital creates heat and noise - the computer I am using right now is really very noisy but it doesn't stop me using it for audio. The trick is to 'tune it out', 'drown it out' or just stop noticing it! I guess DVD players/recorders are not designed to be too close in use (more 'over by the telly' ?) - perhaps you got a bad 'un or you have sited the device badly where it runs hotter than necessary? I think it's more usual that the fans don't kick in too often unless they get very hot - FWIW, I have a Panasonic DVDR which I can't say I ever notice is 'noisy', but then I don't use it very often and I don't suffer from 'vinyl noise' except on extreme examples...?? The above is nothing to do with amps per se. But it shows that some companies end up being run by suits, and have development engineers who just produce what they are told by the suits and go home with their paychecks. The spec says nothing about the fan not making a loud noise, so this cheap one is fine... A development engineer who can't deliver the spec. required by his employers is looking at a career change, at the very least... I've also repeatedly witnessed companies who bring out 'new' products distinctly worse than the ones they'd made a year or two before. Different suits and a different R&D team. No internal communications. No clue. The relevant suits and engineers are often isolated from the public and getting contact with them is almost impossible in practice. I think that one can be safely put down to 'market forces at work in the context of the new, cheap Digital Era' - witness the recent decline in quality and ultimate disappearance of the Technics brand... |
how good are class D amplifiers?
"Keith G" wrote in message ... "Arny Krueger" wrote There's nothing wrong with wondering whether or not a full set of conventional measurements are a reliable guide to sound quality in normal listening. It is a question that has been answered again and again, affirming the idea that a full set of conventional measurements are a reliable guide to sound quality. So simple, isn't it? When you are selecting kit, you just buy a heap of stuff where the figures (or, at least, the figures 'as claimed') tell you it'll work and Bob's your uncle! Yet the (hifi) world is full of people who have done just that and who are not happy with the result - time and time again, some of 'em! You'd think it would be impossible to get it wrong, wouldn't you?? I think that with electronics, it is pretty much impossible to get it wrong if you buy on the figures, *provided* that you understand what the figures are telling you *and* that the published figures are reliable. Sadly, specs are rarely comprehensive, seldom if ever give you the methodology under which they were derived, and even with reputable manufacturers, are not always met. When choosing electronics myself, I've chosen on facilities, price and looks from products who's specs are acceptable, and from manufacturers who's reputation is sound. So far, they only problems I've had are with things that are not part of the specification, like Jim's DVD recorder with a loud fan. In my case it was a Sony DVD/VCR combi player who's remote control was incompatible with Sony's own learning remote system. I bought the Sony DVD/VCR unit only because I assumed being Sony, it would be compatible with Sony's remote. Silly me! The only equipment I would listen to before buying would be loudspeakers, and then only in my own room. Having said that, I bought my current Meridian D5000s sight-unseen, being familiar with Meridian's previous loudspeakers, and I wasn't in any way disappointed. S. -- http://audiopages.googlepages.com |
how good are class D amplifiers?
"Keith G" wrote in message
"Arny Krueger" wrote (in the context of amplifiers) There's nothing wrong with wondering whether or not a full set of conventional measurements are a reliable guide to sound quality in normal listening. It is a question that has been answered again and again, affirming the idea that a full set of conventional measurements are a reliable guide to sound quality. So simple, isn't it? Not at all. It is almost impossible to find a set of manufacturer's specs for a consumer amplifier, that includes anything like a full set of conventional measurements. When you are selecting kit, you just buy a heap of stuff where the figures (or, at least, the figures 'as claimed') tell you it'll work and Bob's your uncle! Typical of your stupid straw-men, Keith. The topic is amplfiiers, and now you're ranting and raving like a loon about "kit" which as I understand your vernacular, means any kind of audio gear. Yet the (hifi) world is full of people who have done just that and who are not happy with the result - time and time again, some of 'em! That's because they made the same stupid assumptions that you have embodied here, Keith. You'd think it would be impossible to get it wrong, wouldn't you?? Keith, with loons like you misreading everything that's posted, I'm not the least bit surprised. |
how good are class D amplifiers?
"Serge Auckland" wrote in message ... "Keith G" wrote in message ... "Arny Krueger" wrote There's nothing wrong with wondering whether or not a full set of conventional measurements are a reliable guide to sound quality in normal listening. It is a question that has been answered again and again, affirming the idea that a full set of conventional measurements are a reliable guide to sound quality. So simple, isn't it? When you are selecting kit, you just buy a heap of stuff where the figures (or, at least, the figures 'as claimed') tell you it'll work and Bob's your uncle! Yet the (hifi) world is full of people who have done just that and who are not happy with the result - time and time again, some of 'em! You'd think it would be impossible to get it wrong, wouldn't you?? I think that with electronics, it is pretty much impossible to get it wrong if you buy on the figures, *provided* that you understand what the figures are telling you *and* that the published figures are reliable. Sadly, specs are rarely comprehensive, seldom if ever give you the methodology under which they were derived, and even with reputable manufacturers, are not always met. When choosing electronics myself, I've chosen on facilities, price and looks from products who's specs are acceptable, and from manufacturers who's reputation is sound. So far, they only problems I've had are with things that are not part of the specification, like Jim's DVD recorder with a loud fan. In my case it was a Sony DVD/VCR combi player who's remote control was incompatible with Sony's own learning remote system. I bought the Sony DVD/VCR unit only because I assumed being Sony, it would be compatible with Sony's remote. Silly me! The only equipment I would listen to before buying would be loudspeakers, and then only in my own room. Having said that, I bought my current Meridian D5000s sight-unseen, being familiar with Meridian's previous loudspeakers, and I wasn't in any way disappointed. Frankly, I don't see what else you can do if you don't have the budget (or inclination) to put yourself into the hands of a 'hifi specialist who promises to do it all for you. Also, there's a lot of highly impractical advice from a 'certain quarter' here that advises auditioning all sorts of kit kit like the dealers have actually *seen* some/most/all of the Desired Items - let alone stock them and will let you home demo them!! (The only way - what good is a 'shop demo'?) All very good in theory, difficult to do in the real world... For me, half the fun is trying to wring a decent sound out of cheap/secondhand crap and/or homebrew and there are those who would say I've had my successes. It's hardly a question of economics I might add - if I had trusted a 'specialist' to throw a system together a few years ago it would have almost certainly saved me a lot of time and money!! My methodology is to buy stuff on spec (yes, the figures matter here - what else is there to go on?), heap it up, sort through it at my leisure and run comparisons over weeks/months - latest candidate is a nice little valve pre that hasn't distinguished itself yet (other than on my Dynacos). It was the right price, looks the business and has definitely got posh innards - my money's on it dropping in somewhere reet nicely at some point... Now, having mentioned that - a 'tubie question': if the afore-mentioned pre has 6SN7GTBs fitted, can I substitute 6SN7GTs as a straight drop-in? Duncan says 'different rating or performance' but the 'Application Data' figures appear identical for both valves?? |
how good are class D amplifiers?
"Serge Auckland" wrote in
message I think that with electronics, it is pretty much impossible to get it wrong if you buy on the figures, *provided* that you understand what the figures are telling you *and* that the published figures are reliable. Right - that's the same think we've been trying to explain to Keith and his fellow loons for a dog's age. Sadly, specs are rarely comprehensive, seldom if ever give you the methodology under which they were derived, and even with reputable manufacturers, are not always met. Totally agreed. Particularly true of consumer electronics. When choosing electronics myself, I've chosen on facilities, price and looks from products who's specs are acceptable, and from manufacturers who's reputation is sound. Been there, done that and it also worked. So far, they only problems I've had are with things that are not part of the specification, like Jim's DVD recorder with a loud fan. In my case it was a Sony DVD/VCR combi player who's remote control was incompatible with Sony's own learning remote system. I bought the Sony DVD/VCR unit only because I assumed being Sony, it would be compatible with Sony's remote. Silly me! Sony does some of the weirdest things, especially lately. The only equipment I would listen to before buying would be loudspeakers, and then only in my own room. Having said that, I bought my current Meridian D5000s sight-unseen, being familiar with Meridian's previous loudspeakers, and I wasn't in any way disappointed. I bought my last 4 sets of speakers either unheard, or heard and thought they sounded pretty poor in the demo room. |
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