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Thread: Audible Jitter/amirm vs Ethan Winer

  1. #71
    Quote Originally Posted by amirm View Post
    I this case, they don't say anything bad .

    A digital source conveys two types of information:

    1. The PCM samples. If something goes wrong with these, you get glitches and audio drop outs. These failure modes are not of interest to us so we can assume all is well here if the music keeps playing.

    2. The timing of said samples. If the sound changes, and #1 is not impacted, then by induction, it is the timing of the samples which is impacted and hence jitter is the sole reason for audibility differences.

    If you read my posts though, you often see me mix in the term "other distortion" to talk about downstream conversion issues which indeed wind up being the sum of jitter and DAC non-linearities. There, we can't distinguish between the two without measurements (and even then it may be challenging at times).
    In your example, it could also be electrical noise from the transport (unless it is connected via optical or well-isolated) getting into the analog signal. If there is anything I've learned in my explorations of audiophilia, it's that even when it is simple, it's not simple.

    P

  2. #72
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    Quote Originally Posted by Ethan Winer View Post
    I agree, and I have learned to say "at normal levels" when discussing jitter and dither and the benefit of 24-bit recording. I'm pretty sure I never said "jitter is never audible in any circumstance," but if I did I meant any normal circumstance.
    I just did a quick web search on your name and jitter and the second Google link said this: http://www.skeptic.com/eskeptic/10-01-06/

    "Digital recorders have a unique type of timing deviation called jitter, but with all modern equipment, jitter is so much softer than the music that you’ll never hear it. "
    Now, don't go searching for me and what I have said in the past or surely you will find skeletons like this and then some .

    I sleep in peace if I have gotten you to move from "never" to "normal circumstances." If everyone did away with extreme views of this field on either side, we would all be happier for it!

    There is no question that we are talking small distortions here. So I am happy to concede as I have repeatedly that this is hard stuff to hear although let's not confuse having to to turn up the volume to train yourself to hear it than actual listening tests post that. I also object to saying that we should all listen to music that is normalized and follows "normal circumstances." I should be free to turn up the music when it is recorded at softer levels. If I hear jitter there, then it is my business to search for ways to eliminated it.

  3. #73
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    Quote Originally Posted by Phelonious Ponk View Post
    In your example, it could also be electrical noise from the transport (unless it is connected via optical or well-isolated) getting into the analog signal. If there is anything I've learned in my explorations of audiophilia, it's that even when it is simple, it's not simple.

    P
    I grant you that if I didn't know what jitter sounded like as opposed to electrical noise unless you are saying that electrical noise caused jitter in the DAC in which case, the distinction is moot .

    Still, good point.

  4. #74
    Quote Originally Posted by amirm View Post
    I grant you that if I didn't know what jitter sounded like as opposed to electrical noise unless you are saying that electrical noise caused jitter in the DAC in which case, the distinction is moot .

    Still, good point.
    No, I'm talking about electrical noise that is distinct from jitter. I've had to answer for why I don't hear differences between digital audio players or hard drives on isolation plinths sending identical data to identical systems. Those who believe they do hear such things are quick to accuse my hearing or the quality of my equipment. I know better, so I have learned to briefly summarize that digital players move data from one place to another within a system and if the error corrected data is the same at the DAC as it is on the original file, there are only two opportunities for it to sound different - electrical noise and timing errors.

    Of course timing errors are not audible under "normal" listening conditions , and my systems is very well-isolated, so I guess there's nothing left to blame but my hearing. By the way, of course you have the right to crank quietly recorded material up, but I still don't think that's going to make the jitter in competent digital devices audible. I believe (cannot prove, but believe) that to hear jitter in such devices you will need to crank the quiets passages up to a point where the crescendos would threaten your hearing, your voice coils, or both. And they would probably have to be the voice coils in your headphones unless your listening room is an anechoic chamber and your speakers are both active and remarkable. Which means, to summarize my personal position on this subject, that while I will concede that unusually bad jitter might be audible under extreme circumstances, it is, in practice, a non-issue.

    P

  5. #75
    [WBF Founding Member] Ron Party's Avatar
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    Quote Originally Posted by Phelonious Ponk View Post
    Of course timing errors are not audible under "normal" listening conditions , and my systems is very well-isolated, so I guess there's nothing left to blame but my hearing. By the way, of course you have the right to crank quietly recorded material up, but I still don't think that's going to make the jitter in competent digital devices audible. I believe (cannot prove, but believe) that to hear jitter in such devices you will need to crank the quiets passages up to a point where the crescendos would threaten your hearing, your voice coils, or both. And they would probably have to be the voice coils in your headphones unless your listening room is an anechoic chamber and your speakers are both active and remarkable. Which means, to summarize my personal position on this subject, that while I will concede that unusually bad jitter might be audible under extreme circumstances, it is, in practice, a non-issue.

    P
    This directly ties in to my Post #63 of which (hint, hint, errr, hmm, pssst: Amir?) I'd like to see more discussion, namely: (1) the detection of jitter while listening through loudspeakers (2) at *normal* listening volumes and (3) as you stated, PP, the detection of jitter while listening to *competent* devices, which includes plenty of gear with measured jitter specs of less than 250 picoseconds.

  6. #76
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    I have nothing to add technically, but I would like to laud and validate the nature of the thread.

    This MUST be the most polite, rational and coherent debate I have ever seen on a forum that touches on anything remotely contentious. And, as a result of this, it must also be the most educational.

    Thankyou, looking forward to many more like this.

    I too would like to see the emphasis now switch to 'less contrived' circumstances, real world, real rooms, real systems that we use.

  7. #77
    Quote Originally Posted by Ron Party View Post
    This directly ties in to my Post #63 of which (hint, hint, errr, hmm, pssst: Amir?) I'd like to see more discussion, namely: (1) the detection of jitter while listening through loudspeakers (2) at *normal* listening volumes and (3) as you stated, PP, the detection of jitter while listening to *competent* devices, which includes plenty of gear with measured jitter specs of less than 250 picoseconds.
    Yes, but be careful. We could very quickly get to a place where we'll be concluding that properly implemented DACs, integrated into very common consumer electronics should be transparent and, therefore, audibly identical to even the most esoteric products. And that's just a short step away from concluding that many are transparent, and we may find a lot of people very resistant to that notion.

    P

  8. #78
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    Speakers present challenges and perhaps some opportunities for hearing digital distortion:

    - One speaker can mask distortion in the other. Let's say there is a 2 Khz jitter sideband and nothing close to it in that channel but the other, has a strong 3 Khz signal in it. The latter will mask the former. Headphones eliminate this chance.

    - There is less in an audio chain with headphones directly driven by a DAC or source with its internal DAC. There is no power amp. There is no crossover. There are no speaker wires.

    + Speakers do have the advantage of providing imaging. If you have crosstalk issues between channels (e.g. in low cost stereo DACs), you may be able to hear that better than with headphones.

    On jitter being less than 250ps, keep in mind that the math makes some simplifications to get there. Namely, it assumes jitter is a simple sine wave. If a DSP pluses the system once every millisecond causing the jitter to have a spectrum similar to that, that math doesn't apply. Also keep in mind that the number is driven based on bandwidth of 20Khz and sample resolution of 16 bits. If you listen to high res music, then you need to follow much strictly timing spec than this number.

    As to equipment today being competently designed, and jitter not being an issue, you can only say this if you have seen their measurements and not manufacturer's claims of jitter numbers. But sure, if you can interpret a chart like this, you are golden:


  9. #79
    Member Sponsor [Technical Expert] DonH50's Avatar
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    Hmmm...

    1. I understand the spatial imaging aspect, but am not sure why crosstalk would be easier to hear with speakers? I have always used the cans for that (actually, unless it's pretty bad, I resort to a 'scope or other test equipment to measure crosstalk). However, I usually do it "old school" by putting a full-scale signal in one side and terminating the other input, then measuring (or listening to) the "off" side to see (hear) what gets through.

    2. In the "normal" math I have seen, jitter is treated as white noise, or perhaps broken into various types of colored noise depending on distance from carrier on a phase noise plot in an RF sampling system (have not seen that in audio, or very rarely). The signal, however, is usually assumed to be a single-tone sinusoid at full-scale to generate the most often-used jitter formula relating SNR degradation and jitter, e.g. this one from an ADI app note:

    SNR = 20*lo(2*pi*fin*tj) where
    pi = 3.141592654...
    fin = input signal frequency
    tj = amplitude of time jitter

    For random jitter, the SNR is related only to the input signal frequency and jitter amplitude (in time). System bandwidth does not enter into it, and resolution and signal amplitude falls out of the equation. I agree that the math is invalid if these assumptions are not valid, e.g. the math does not work properly if:

    a. The jitter is not (or can not be statistically treated as) white noise;
    b. The input is not a pure sinusoid;
    c. Even for a pure sinusoid, the equation is not valid over the entire period of the signal due to changing slew rate at different points on the sine wave, but the average is good enough;
    d. There are no other noise or error sources in the system;
    e. Sampling is perfect, with only time jitter added.

    Plus other assumptions I've forgotten and others can point out, but I need to get to bed. IMO - Don
    Don Herman
    "After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
    Don's Technical Articles on WBF

  10. #80
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    Quote Originally Posted by amirm View Post
    You need to trust me that I know the difference
    Since you know the difference, that's all the more reason to use the correct terminology when reporting.

    So let's move on and talk about other points. I think we have beat this one to death.
    Agree. I see this excellent discussion has moved on and IMO, that's great to see.

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