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Hard Disc Player Sound Quality
On Sat, 24 Jan 2004 09:42:02 +0000 (GMT)
Jim Lesurf wrote: Yes. In that what really matters is that the data samples are converted into analogue output at (ideally) perfectly regular intervals. Otherwise you would be distorting the output by adding a form of phase modulation. If you can't do this, then all else is a bit futile. Of course. No. In that there is a slight risk that jitter might be so bad as to cause a bit to be lost (or duplicated) on the way to the DAC somewhere. I really doubt this happens with any regularity, even on spdif ;-) In practice I assume that decent players/DACs employ suitable buffering, etc, to be able to ensure that the data is read from the disc reliably. Wel, an outboard (spdif based) DAC has the problem that it cant feed back to ensure the data is reliable. but yes, for a CD player thats true. Can cable length increase jitter? What really matters here is the non-dispersive bandwidth of the cables. Ok. The S/PDIF waveform mixes together both the data pattern and a clock signal. Yes, I know that. *IF* the receiver uses the timing of the 'edges' of the waveform as it clock indication the result is that the apparent clock will then jitter with the data pattern *even if the source had a perfect clock*. Ugh. surely no-one tries to use the raw waveform as the clock? In the event described above, the receiver might then produce irregular output samples, and the sound becomes modulated by the effect of the finite bandwidth or dispersion of the cables used, via the daft use of the signal edges as the clock. Surely only the cheapest DACs do this? In most cases in practice, though, I doubt this should matter much. :-) agreed. If not, then I doubt it matters where you place the clock. In fact, for audio use, Im sure it doesnt matter, as Jodrell bank does radio interferometry using much higher frequencies over far greater distances, which also requires a synchronised time source. That is different for various reasons. The key one is that the clock is kept *seneparate* to any data. Yes, quite - I was referring at that point to Stewarts 'synchronous bus' system, which also seperates the clock. The reference clock is sent between antenna stations in a way that is not 'corrupted' by data transfer. Would be a bit pointless if it wasnt ;-) The S/PDIF system (and various comms systems) puts the clock and data together to use a single channel. Yes, I know. In theory, it does not matter where, physically, you locate the master clock. However this is 'provided you can pipe it around with no problems due to noise, etc'. Yes, that was my question - as to wether cabling FWIW the longest baselines I know of were back in the Pioneer/Voyager days. The spacecraft transmitter was phase locked to the signals it received from Earth (I think the ratio was 222/221 or some-such.) Thus here the phase lock was acheived over a loop distance greater than the diameter of the major planets of the solar system! :-) That is rather cool :) or via carrying 'atomic' clocks about (which has other problems). Such as relatavistic effects due to being on a plane ;-) Surely if you design a good atomic clock you have a stable frequency reference, and so all you need to do is build two clocks and adjust the phase? What strategies do they use to synch atomic clocks? Or, more to the point, whats the highest frequency they can work with now - I assume the degree of synchronisation defines the effective precision of the baseline, and thus the minimum wavelength they can reliably use for interferometry ? There the baselines are typically a few thousand km. I had heard GPS could be used as a frequency reference for this - but have no idea how good it is, beyond knowing its good enough to have to care about relatavistic effects. -- Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux Do not meddle in the affairs of Dragons, for you are tasty and good with ketchup. |
Hard Disc Player Sound Quality
In article , Ian Molton
wrote: On Sat, 24 Jan 2004 09:42:02 +0000 (GMT) Jim Lesurf wrote: *IF* the receiver uses the timing of the 'edges' of the waveform as it clock indication the result is that the apparent clock will then jitter with the data pattern *even if the source had a perfect clock*. Ugh. surely no-one tries to use the raw waveform as the clock? Probably not, in simple terms. However the problem is that the source clock is 'buried' in the S/PDIF stream, so that stream is what you're given and then you have to devise a suitable way to extract a suitable clock. Hence you can apply careful design, but you have the problem to deal with if receiving S/PDIF. Surely if you design a good atomic clock you have a stable frequency reference, and so all you need to do is build two clocks and adjust the phase? The snag with atomic clocks is that you are using line frequencies that were chosen precisely on the basis that nothing much affects the frequency you get. Hence tweaking their output can be awkward. This is a consequence of something Stewart has pointed out. VCOs tend to have more phase noise than 'fixed' oscillators. The tuning mechanism will have noise, and this then ends up noise-modulating the frequency. Hence you're more likely to build two clocks, get them stable, and then calibrate their phase/frequency differences by comparing their outputs over a long enough period. In general you can count cycles as well, so you can break the comparison for a while and come back later. What strategies do they use to synch atomic clocks? See above. It tends to be more a process of comparisions and cross-calibrations. Not up on this, but I think the best modern clocks use things like ion traps with laser 'cooling' of the atomic population. However this isn't field, so I'm just trying to recall tea-time conversations I've had with people over the years! :-) Or, more to the point, whats the highest frequency they can work with now - I assume the degree of synchronisation defines the effective precision of the baseline, and thus the minimum wavelength they can reliably use for interferometry ? Don't know the current state of the art. However I think people now do few hundred GHz arrays over the order of a km, and lower frequencies over much wider baselines. One of the problems here, though is data bandwidth, not the center frequency. Hence it isn't so much the center frequency you're using that may be the limit, but the tendency for astronomers to want GHz's of data bandwidth. If you drop the bandwidth you can often go to a longer baseline. But if you drop the bandwidth you end up with less information from what you are trying to look at. Pays yer money and takes yer choice... :-) There the baselines are typically a few thousand km. I had heard GPS could be used as a frequency reference for this - but have no idea how good it is, beyond knowing its good enough to have to care about relatavistic effects. I suspect that GPS would have too poor a short-term phase stability for 'direct' use due to atmospheric propagation errors. However they may use it for medium and long term reference checks on the 'local' clock used at any antenna station. Countries like the USA, UK, etc transmit clock signals by radio as well for these purposes. Rugby MSF is the one most people know about and the long term accuracy of this should be good. There are loads of these all around the world, though, often at a few MHz IIRC. However I'm not in this area, so you'd need an up-to-date radioastronomer to say what methods they use in detail these days. 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 |
Hard Disc Player Sound Quality
On Sat, 24 Jan 2004 11:08:55 +0000, Ian Molton wrote:
On Sat, 24 Jan 2004 07:48:53 +0000 (UTC) (Stewart Pinkerton) wrote: Demonstrate Im not. Show me one reference I made to a specific DAC and the way it works. Yeah, like I said, pathetic. I note theres no reference cited there... Of course not, because you initially screwed up, and are now trying to duck and dive your way out of it by pretending you were really just talking about what is theoretically possible, in classically childish Max Christofferson style. Grow up. Jim has provided (as usual) an excellent synopsis of how it all works - he has far more patience than I, possibly due to years of exposure to similarly immature students! -- Stewart Pinkerton | Music is Art - Audio is Engineering |
Hard Disc Player Sound Quality
On Sat, 24 Jan 2004 17:38:45 +0000 (GMT)
Jim Lesurf wrote: Probably not, in simple terms. However the problem is that the source clock is 'buried' in the S/PDIF stream, so that stream is what you're given and then you have to devise a suitable way to extract a suitable clock. Hence you can apply careful design, but you have the problem to deal with if receiving S/PDIF. I would think that a good system would be something like this: 1) Extract the data (dont care how) whilst buffering the input samples used (inc. embedded clock). 2) Strip the data from the input samples now that we have decoded data and the original samples, leaving only the clock 3) use a PLL to lock onto this clock and provide a stable reference. Surely this woiuld give you a clock signal with only an absolutely minimal amount of jitter (potentially less than the source clock). Im not arguing it would be better than a single reference clock fed to all components, but it should eb pretty damn good... -- Spyros lair: http://www.mnementh.co.uk/ |||| Maintainer: arm26 linux Do not meddle in the affairs of Dragons, for you are tasty and good with ketchup. |
Hard Disc Player Sound Quality
"Jim Lesurf" wrote
I suspect that GPS would have too poor a short-term phase stability for 'direct' use due to atmospheric propagation errors. However they may use it for medium and long term reference checks on the 'local' clock used at any antenna station. Countries like the USA, UK, etc transmit clock signals by radio as well for these purposes. Rugby MSF is the one most people know about and the long term accuracy of this should be good. There are loads of these all around the world, though, often at a few MHz IIRC. Isn't Rugby at some very low frequency like 60 kHz? I have one of thos increasingly ubiquitous mini radio-"controlled" alarm clocks. Th'******* woke me up in the middle of the night recently. The alarm was set for 07:00 but it woke me at 01:00 or something. Dunno what happened, or why it did it, but it scared the living crap out of me: "What? It can't be time to get up already! Oh NOOOO. No, not now!" I guess it must have messed up when syncing itself at midnight or something. Imagine my relief when I finally worked out that it wasn't time to get up! Scary though! What made it do that?! Maybe a ghost or something! Aaarggh!! (And I don't even believe in ghosts, but I can get very scared at night in the dark, alone.) Martin -- M.A.Poyser Tel.: 07967 110890 Manchester, U.K. http://www.fleetie.demon.co.uk |
Hard Disc Player Sound Quality
On Sun, 25 Jan 2004 18:33:26 -0000, "Fleetie"
wrote: "Jim Lesurf" wrote I suspect that GPS would have too poor a short-term phase stability for 'direct' use due to atmospheric propagation errors. However they may use it for medium and long term reference checks on the 'local' clock used at any antenna station. Countries like the USA, UK, etc transmit clock signals by radio as well for these purposes. Rugby MSF is the one most people know about and the long term accuracy of this should be good. There are loads of these all around the world, though, often at a few MHz IIRC. Isn't Rugby at some very low frequency like 60 kHz? Yes. -- Stewart Pinkerton | Music is Art - Audio is Engineering |
Hard Disc Player Sound Quality
Gelf wrote in message . ..
PC based hard disc players seem to be a common topic of discussion in this ng at the moment Has anyone any comments on likely sound quality compared to a standalone CD player? I'm thinking along the lines of feeding digital audio from a PC soundcard via optical link to a standalone Musical Fidelity DAC, then to amp and speakers. The CDs would be stored on the hard disc as wav files or flac (lossless compression) My current CD player is a Marantz CD6000OSE Gelf I 've done exactly the same thing. Got a new pc, stuck in 4 x 160gb hard drives and ripped my 700 or so cds as WAV files using EAC. An optical out connects to a DAC and into my STAX phones and the sound is awesome - at leaste the equal of any CD player I've ever owned (up to £500ish). The convenience and ease of use is incomparable. Once you get into creating playlists etc, there's no going back. I sold my cd player, and a stack of CDs that I really have no pride of ownership in, and I'm quids in. So much so, I treated myself to an iPod! |
Hard Disc Player Sound Quality
"Keiron" wrote I 've done exactly the same thing. Got a new pc, stuck in 4 x 160gb hard drives and ripped my 700 or so cds as WAV files using EAC. An optical out connects to a DAC and into my STAX phones and the sound is awesome - at leaste the equal of any CD player I've ever owned (up to £500ish). The convenience and ease of use is incomparable. Once you get into creating playlists etc, there's no going back. I sold my cd player, and a stack of CDs that I really have no pride of ownership in, and I'm quids in. So much so, I treated myself to an iPod! Ha! Nearly posted the same thing (more or less) a few days back - if you are going to listen to digital, what better way than straight from a PC, through a DAC into a valve amp (my own preference :-). Vinyl ripped to hard disk sounds particularly good and the accessability of hundreds (or thousands) of tracks at a click or two means you can really rediscover those forgotten little gems and can track-hop like a good 'un! On this topic, a word to the wise...... taps side of nose with extended forefinger ....... don't go tearing into your local HiFi Robber Baron's yelling 'I wanna DAC, I gotta have a DAC'!! Atm, these ole boys think they can't give 'em away secondhand (these and graphic EQs) so they are priced reet cheap. Make a fuss and you'll double the price!! Best to sidle up and act a bit dim - 'what's this then? what's it for....???' :-) |
Hard Disc Player Sound Quality
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Hard Disc Player Sound Quality
Gelf wrote:
I 've done exactly the same thing. Got a new pc, stuck in 4 x 160gb hard drives and ripped my 700 or so cds as WAV files using EAC. An optical out connects to a DAC and into my STAX phones and the sound is awesome - at leaste the equal of any CD player I've ever owned (up to £500ish). The convenience and ease of use is incomparable. Once you get into creating playlists etc, there's no going back. I sold my cd player, and a stack of CDs that I really have no pride of ownership in, and I'm quids in. So much so, I treated myself to an iPod! What playlist software are you using? I have the same sort of setup as above and use iTunes. It's got a really neat 'Smart Playlist' feature where you define the criteria for inclusion in a playlist and iTunes itself then adds tracks to the playlist as you rip new CDs. Once you've defined the playlist criteria (Genre, Type, etc etc) you never need touch playlists again! |
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