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