Untitled Document

Page 4 of 18 FirstFirst 1234567891011121314 ... LastLast
Results 31 to 40 of 175

Thread: Audible Jitter/amirm vs Ethan Winer

  1. #31
    Banned
    Join Date
    Jul 2010
    Location
    New Milford, CT
    Posts
    1,232
    Quote Originally Posted by amirm View Post
    Until then, you could simply avoid the concern altogether and simply buy equipment with less than 250ps worth of jitter
    Well, even the worst performer in the bunch was 13.7 times better when using the SPDIF output than your worst-case example of the Yamaha using HDMI. So the better lesson is to not use HDMI for audio. But your point is taken. I don't use HDMI for audio and wasn't aware how bad it could be. I'm still not convinced that such level of jitter would be noticed in a blind test. Too bad you live so far because I'd like to test this with you together in person.

    --Ethan

  2. #32
    Banned
    Join Date
    Apr 2010
    Location
    Seattle, WA
    Posts
    16,044

    Jitter Audibility Summation

    Thanks Ethan for the fun debate. While I have argued these points on many other occasions, the one-on-one nature made it much easier to convey the information.

    As I said at the outset, I don’t believe that it is possible to prove that jitter is audible in all conditions and for all people. Indeed, quite the opposite is true that for most people, most of the time, jitter and other ills of digital audio are not a concern.

    Audibility of jitter is a tough topic because as a general rule, people don’t know what it sounds like. So often, that is the first reason put forth on why it doesn’t matter: “I have tested it and I don’t hear it.” To which I ask how they tested it and it becomes clear that they don’t know how to test for it.

    We are naturally trained to hear analog domain distortions. Change the bass level and everyone can tell the difference. Change the volume, and they can tell that too. But what the heck does it sound like when the two lower bits in a 16-bit audio sample are not reproduced well? Does the frequency response change? No. Does the level change? No.

    While some people are born with the ability to sense jitter artifacts, for others they need to be taught what it sounds like before they can spot it.

    The way we train listeners in general to hear digital domain artifacts is to start with gross levels. Play that enough times and the ear and brain learn what it is and then a magical thing happens: you can hear it even when its level is reduced substantially! It is non-intuitive that way but in practice, it works quite well.

    As Ethan noted, it sure would be nice to have a jitter box with a knob you can adjust so that the above training can occur. Alas, such a box doesn’t exist readily because jitter has infinite variations. And even if it existed, it would not something people everywhere would own.

    That brings me to the subject of using compressed music as way to learn to hear such artifacts. As Ethan's reaction indicated, at first blush, it seems odd that hearing audio compression artifacts helps you with hearing things like jitter. But I can speak from personal experience in saying that it completely opened up my hearing ability to not only detect digital audio distortions but also many other subtle audio differences even under the constraints of double-blind environment. I think it has something to do with learning to find things that are wrong or different, rather than just listening to music as we all instinctively do (even when we think we are auditioning something).

    There is another notable thing about compressed music: its distortion is correlated to the content. For example, if you have a transient, it gets distorted with grunge in front of it (we call that pre-echo). Feed it steady state signal and that doesn’t happen. Correlated distortion can be quite annoying. The brain tends to be bothered more by distortion that comes and goes than one that stays the same. This is why I said the paper should have used this type of jitter, not one that is akin to noise.

    The second point often made is that today’s digital gear is so good that jitter and for that matter, any other digital distortion is immaterial. To which I ask, “how do we know?” The paper makes that claim without a single bit of back up. It doesn’t even show the measurement for one device let alone all devices.

    We know the mathematics of jitter tells us that if we want to resolve 16 bits and allow a bandwidth of 20 KHz, jitter must be exceeding small -- in order of 250 ps (250 trillionth of a second). As small as that is, if you increase bandwidth (e.g. as in higher sampling rate audio) or higher bit depth (e.g. 24 bits instead of 16) the number has to be even lower! All the gear that I listed from HiFi magazine claim to play 24-bit, 192 KHz audio. Yet in most cases their jitter alone dictates that they can barely resolve 16-bit audio at 44 KHz sampling let alone anything higher. Most mass market gear is linear to 14 bits or so after which, they start to distort digital samples.

    Of note, the 250 ps assumes sinusoidal jitter not because that is the type of jitter we have in audio equipment but because it is easier to do the math that way. Jitter could have very different profiles and as such, its level may have to be even lower than this simplified math shows.

    The above discussion does away with the second objection against importance of jitter. That somehow, sampling theory says digital is perfect. Sampling theory does indeed say that but it assumes an idealized system that is free of distortions such as timing of samples varying by one or more factors.

    So what does jitter, or for that matter, other digital distortions sound like? The first clue is that you will lose the sense of space around notes. This happens because the sense of space comes from reverberations which are far lower in level than the main signal (the sound weakens as it bounces around the space). Because their levels are lower, they rely far more on the low order few bits of the 16-bit audio samples to be accurate to sound good or be heard at all.

    The second symptom is increased accentuated high frequencies which can sound harsher. This occurs for two reasons. One, jitter damages higher frequency signals more than low frequency ones. A low frequency signal doesn’t change as much over time so if timing varies, it is less impacted. High frequency signal jumps around more which makes it more important to reproduce samples when they are supposed to. Think of it as how sensitive your steering wheel is in the car when driving very fast as opposed to barely moving.

    Second reason high frequencies are impacts is because jitter distortion created in lower bands, manifests itself at higher frequencies. If a 2K Hz jitter is applied to a 5 KHz signal, its artifacts show up at 3 KHz and 7 KHZ. The latter lands on top of fainter high frequency content in your music, causing its energy to increase even if it is not directly audible. That increased energy will make the sound brighter.

    So the trick to hearing jitter easier is to combine the above two. Find a signal that is quiet (to get rid of masking effect), has ambiance, and some sharpness to it. A single pluck of guitar that goes to nothing is a good on as is a lonely cymbal crash. I suggest using headphones so that you remove room effects. Set up your player to loop on that note, turn up the volume to be loud so that you can hear the end of the decay but not so loud as to damage your hearing. Once there, modify things that can impact jitter such as turning off your AVR video circuits and front panel display. Or switch between DACs for transports. With practice, you should start hearing the artifacts.

    At this point Ethan will say that if you have to turn up the volume, then it doesn’t matter. But as I said before, the above is for training. Once you learn the artifact, you will be able to spot it in lower levels. That said, there is no question that if your music is loud and playing at near 0db, jitter is not a consideration. As I noted in the posts, digital is perfect at playing loud. Ask anyone who plays their home theater even on cheap hardware and they rave about it shaking the floor! It is the subtle tones where digital starts to struggle some.

    The good news here is that you can impact jitter. Changing to a digital transport or the way samples are moved from one place to the other can make a big difference. This is why people have invented things like “asynchronous USB” DACs for PCs. I showed example of changing from HDMI to S/PDIF or going from one brand to another.

    While Ethan did not go there, many electrical engineers put forth another defense: why not read a lot of data into a buffer (piece of memory), and then output the samples one by one using a very accurate clock. Unfortunately we can’t do that outside of a studio. Our systems need to stay in sync with upstream sources and that forces the DAC to follow the timing errors of ahead of it, not its own independent clock.

    Think of a Blu-ray player playing a concert. The video clock drives the system timing and audio samples are slave to it. There are X audio samples for each frame of video. Your AVR doesn’t get to buffer those audio samples in its memory and to send it out using its own clock. If it did that, it would over a few minutes, drift from video clock and you lose lip synch. Yes, this happens even with ultra-accurate crystal controlled clocks.

    There are techniques such as dual PLLs to lock to incoming signals at high accuracy while filtering jitter. But such circuits tend to be expensive as they have to be discreet in nature. This is why I said that there is merit in higher end DACs in this space as that kind of attention is paid to jitter and low level digital distortions.

    Note that measuring jitter is an expensive proposition. It requires equipment which costs $25K such as my Audio Precision analyzer. Be wary of people who make claims of jitter reduction who don’t have such equipment. Great example is the many companies which modify video players such as Oppo with better clocks, power supply and such. There is no guarantee that a bigger, better, linear power supply improves things. It may actually make things worse! Demand to see their before and after jitter specs including measurement charts.

    Let me also touch again on the PC audio situation. PC can make a wonderful music source. Beyond all the convenience features, by ripping your music and putting it on the hard disk, you rid yourself of the clock that the DAC must lock to in the serial digital stream on the CD. Data is read asynchronously from the hard disk or solid state disk with no clock to speak of, putting you a step head.

    Unfortunately, as soon as you output those samples, you are back to having a clock to go with it. That clock can be supplied externally or internally. In the standard method of playing something over S/PDIF, the clock is supplied by the PC and can be subject to jitter of all types. So you are back to having to deal with this issue. DACs that use async USB avoid this problem by having the external device drive audio samples in the PC.

    Putting it all together, jitter is indeed a small level of distortion. It is not a problem for the general public or those with very limited funds to deal with it. For discerning audiophile though, it should be a consideration. Investing in good gear with good digital hygiene, can help eliminate it, bringing digital closer to its ideal characteristic of being transparent to the source.

  3. #33
    Banned
    Join Date
    Jul 2010
    Location
    New Milford, CT
    Posts
    1,232

    Lightbulb

    Jitter Audibility Summation

    This exchange with Amir has been a lot of fun! I really appreciate the chance to debate technical aspects of audio one-on-one without interruption. Versus what happens so often in other forums where people having nothing of substance hurl insults and worse.

    Amir said "I don't believe that it is possible to prove that jitter is audible in all conditions and for all people." But that's never been the issue. All I ask for is evidence that any type of jitter is ever audible under any circumstance. It's also a logical fallacy to ask someone to prove a negative. The burden of proof is on those who make a claim. I have asked repeatedly for evidence that jitter is ever an audible problem. Not just here in this exchange with Amir, but I've asked for this for years. If a jitter proponent claims that jitter can be audible, all they have to do is prove it. Use any type of artifact you want. Correlated, uncorrelated, trebly buzz, bassy IMD-like grunge - anything you feel proves your position using the worst-case artifacts you can muster. Turn it on and off to make it even more audible if you feel that better proves the point. It doesn't have to be a test that I can pass either. If some people can recognize jitter more readily than others, I'm glad to have them prove it in a proper blind listening test. As far as I know this has never happened.

    Amir said you can learn to hear jitter by changing between DACs, but that proves nothing. There could be other reasons two DACs sound different. Further, it's likely that two DACs that are reported sounding different do not in fact sound different. It's common knowledge that people will report hearing a difference even when nothing has changed. As I mentioned earlier, in a recent test I was involved with I goofed a file export, and two of the three files (B and C) being judged were in fact bit-identical. Yet half a dozen people reported obvious differences between the files. Here are just two examples:

    "My opinion is that file B sounds significantly better than the other two files.
    A sounded the worst to me, and C came in second place."

    "I found the difference between A and C not so big as between B and A/C."

    I have tested artifact audibility many times, and have never been able to hear things 80 dB below the music while the music plays. Even under the most favorable conditions. So the "problem" associated with jitter is to me an extraordinary claim that in turn demands extraordinary proof. As far as I know, no such proof has ever been offered anywhere let alone in this thread.

    I was surprised to learn that HDMI audio is as bad as that Hi-Fi magazine measured. I come from the pro audio world where people often claim that jitter is a problem with sound cards and converters. But I doubt that even the high levels of jitter the magazine measured over HDMI is ever audible. Amir said such levels of jitter reduce the s/n ratio, but that's not really true. A more accurate metric is to consider jitter a distortion artifact because it comes and goes with the music. Using Amir's Audio Precision graph showing jitter sidebands at "only" 80 dB down equates to a distortion figure of 0.01 percent. This is consistent with the distortion amounts one gets from high quality audio gear. And vastly lower than any loudspeaker I know of. Further, that AP graph is not realistic because it uses a 10 KHz sine wave at 0 dBFS as a test signal. As Amir himself said (Post #20), "Show me where high frequency content is at 0db and I buy your arguments."

    I also dispute the notion that jitter can affect imaging and sound stage. In my experience as a professional recording engineer, the level for adding a just-barely noticeable amount of reverb is around -20 dB. Adding reverb at -40 is totally useless and does nothing. So the notion that jitter affecting the lowest bit or two can effect spaciousness is highly unlikely. I file such reports in the same bin as reports of a difference in an A/A test.

    In the grand scheme of things, this is a consumerist issue. We are asked to pay more - often much more - for gear that claims lower jitter than the competition. But even cheap digital gear has jitter low enough to not be audible. Versus the obvious and highly audible difference between loudspeakers, not to mention poor room acoustics which the majority of "discerning audiophiles" blindly ignores.

    I do agree with Amir that manufactures who claim low jitter need to prove it. If every unsubstantiated claim was accepted without question, we'd all sprinkle magic pebbles around the room, stick little paper dots on our windows, and carefully demagnetize all of our LP records.

    --Ethan
    Last edited by Ethan Winer; 08-07-2010 at 01:52 PM. Reason: Sorry! One last point, about imaging

  4. #34
    [WBF Founding Member] Moderator RBFC's Avatar
    Join Date
    Apr 2010
    Location
    Albuquerque, NM
    Posts
    5,090

    Opening thread for comments and questions

    Since both participants have submitted "summary" statements on this topic, we can now open up the thread to comments and questions from all interested parties. I ask that we keep this civil and impersonal as we proceed. If you don't agree with one individual, direct questions at the statement(s) with which you disagree, not at the individual.

    We are fortunate to have industry experts in many fields here to discuss these matters, so please offer the utmost in respect for their kind donation of time and information.

    So, who would like to inquire about anything contained in this discussion?

    Thanks,

    Lee

  5. #35
    [WBF Founding Member]
    Join Date
    Apr 2010
    Posts
    848
    Really enjoyable to read a debate conducted this way without all of the clutter that you usually see on A/V sites with drive by graffiti, insults, and off topic distraction.

  6. #36
    Member Sponsor [Technical Expert] DonH50's Avatar
    Join Date
    Jun 2010
    Location
    Monument, CO
    Posts
    3,517
    I already put in my two cents... I am working on doing some plots and explanation along the lines of the units and terms, sampling, and aliasing threads over in the Tech Forum. Not as a debate, but to (hopefully) help out some of us a bit confused by all the jitter talk around here... - Don
    Don Herman
    "After silence, that which best expresses the inexpressible, is music" - Aldous Huxley
    Don's Technical Articles on WBF

  7. #37
    Banned
    Join Date
    Apr 2010
    Location
    Seattle, WA
    Posts
    16,044
    While we are waiting for questions , I just wanted to clarify for Ethan that all of the testing I have mentioned in this thread were double-blind and repeatable in independent trials with the conditions changed to force an alternate outcome. The testing also included using the same DAC but changing digital source characteristics. While I am not claiming this rises to the level of convincing others, it certainly convinced me . Doubts about reliability of DBT results when conducted by people in the industry with fair amount of rigor, can be used I am sure to fuel a different debate .

    And a technical correction: when jitter profile is random as was in the paper and your graphs, it serves to raise the noise floor and impacts S/N. You can see that stated below your own graph as highlighted by me now:


  8. #38
    [WBF Founding Member]
    Join Date
    Apr 2010
    Posts
    848
    Quote Originally Posted by amirm View Post
    While we are waiting for questions , I just wanted to clarify for Ethan that all of the testing I have mentioned in this thread were double-blind
    This is interesting. Earlier in the thread you wrote...

    Quote Originally Posted by amirm View Post
    The more rigorous tests I ran were all double-blind. For example, I would test the effect of turning off the video circuit in a digital source (e.g. DVD-A) by turning away from the gear, hitting the switch many times in a row so that I didn't know what state it was in at the end. And then toggle back and forth while listening.
    I've seen you refer to tests like these as "double blind" before. If this is the kind of thing you mean when you say all tests were "double-blind" I think there should be some sort of asterisk to explain that when you say double blind, this is what you mean or else perhaps you should discontinue using the term "double-blind" as this is not exactly double blind. Personally, if I could cast a vote it would be for you to discontinue using the term "double blind" since an actual double blind test requires another level of "blindness." I don't think it helps in terms of clarity of debate to use a scientific term like "double-blind" unless it is truly double blind.

  9. #39
    Banned
    Join Date
    Apr 2010
    Location
    Seattle, WA
    Posts
    16,044
    Quote Originally Posted by rsbeck View Post
    I've seen you refer to tests like these as "double blind" before. If this is the kind of thing you mean when you say all tests were "double-blind" I think there should be some sort of asterisk to explain that when you say double blind, this is what you mean or else perhaps you should discontinue using the term "double-blind" as this is not exactly double blind. Personally, if I could cast a vote it would be for you to discontinue using the term "double blind" since an actual double blind test requires another level of "blindness." I don't think it helps in terms of clarity of debate to use a scientific term like "double-blind" unless it is truly double blind.
    What is true double blind in your opinion and what is not?

  10. #40
    Banned
    Join Date
    Apr 2010
    Location
    Seattle, WA
    Posts
    16,044
    BTW, since I explained what I meant by the term, I don't know why you are asking for a footnote. What I said must have been clear enough for you to say it wasn't valid .

Page 4 of 18 FirstFirst 1234567891011121314 ... LastLast

Similar Threads

  1. Hi from Ethan Winer
    By Ethan Winer in forum Introduce Yourself
    Replies: 8
    Last Post: 07-12-2010, 10:14 AM

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •