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Low-Jitter USB: Dan Lavry, Michael Goodman, Adaptive, Asynchronous

Discussion in 'Computer Audio' started by jude, May 20, 2010.
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  1. bigshot
    Especially if you live in a tiny crowded apartment. It takes a reasonable sized living room and some open space for speakers to sound their best. Headphones are not as bad for synthetic music with electronic instruments and manufactured soundstage. But natural acoustic music like Jazz and Classical always seem to sound much better on speakers. The soundstage of this type of music is usually designed to create an aural proscenium when the sound is coming from in front of the listener. It doesn't work as well halfway between his ears.
  2. mgoodman
    @ CHansen
    > It is possible to get high levels of performance from variable-frequency clocks (generally using a Phase-Locked-Loop or PLL).
    > But not as high as you can get with fixed frequency clocks. That is a fact. Mr. Goodman is peddling deception.
    I got a kick out of that one :)
    No, Mr. Goodman is not peddling deception. Mr. Goodman is using fixed, high quality clocks in his designs, which makes their output jitter very low. Mr. Goodman is not disputing the fixed clocks. This is what I said (slightly paraphrasing):
    The data bursts coming from the computer into the DAC will always be variable, because computers send data in irregular intervals - computers are busy doing many things. However, what *goes out* of the DAC must be clocked in fixed intervals. That's called "clock cleanup". I agree that using a variable clock at the DAC stage is a no-no. We neither use a variable clock nor are we suggesting that you should.
    My point is still correct. With a good Adaptive or Asynchronous implementation, what comes in is irregular (variable), what goes out is fixed. You can say that with Asynchronous it's irrelevant that the data coming in is irregular. I can respond to that by saying that with Adaptive it's also irrelevant, if you clean up the clock. It's irrelevant in both cases, because in both cases the output is clocked with the fixed clock.
    I'm not peddling deception. Please be careful with your assessments :)
  3. regal


    Bad recordings have a huge impact on SQ and evaluations.    Only well mastered material can I hear differences in transports,  do I think I suffer from some sort of psychological predisposition?  No I trust my perception of sound,  coincidentally I prefer the transport with the highest jitter spec over some of the ones with lower (all verified bit-perfect.)   Quick listening tests and studies are worthless,  human perception as a model in the psychological field is very different from that in the neuroscience field.  The soft sciences usually make grand inductions based on a few "far removed from reality tests" when it comes to Audiophile subjects.  Lets face it there hasn't been the research, grants, and dollars spent on audiophile matters in comparison to say psychopathology,  probably less than 1 billionth in research dollars spent as a ratio.  To the point that the studies have little statistical significance and rely on pretty big inductions.  There is also the factor that few people have perfect pitch hearing,  or even decent pitch hearing.  There is the factor of music note memory.  Surely Bach's perception of instruments was different than Jimmy Hendrix.  Do these "studies" take into account musical genius?  Not saying I'm one but each and everyone of us has a small bit,  all different in magnitude and form, I suppose.
    About every day I see a post where someone "claims" to hear a difference in a transport vs another on the internet.  Personally I put more faith in the individual than a few low budget soft science studies.   Now in a few decades when neuroscience/hard science/physics are able to describe the phenomena   o o    of perception called hearing maybe science will have something to offer.  Until then its really just low budget professors trying to make a name for themselves in unsuccessful attempts to get more grant money.  Trust me I have a Yale proffessor for a brother, and a law proffessor for a sister,  I know the games played in strife for grant money.
  4. zenpunk
    I am always amused by nonsensical claims that somehow the mysterious and magical world of audio and Hi-Fi remains misunderstood or escapes the limitation of science.
    Anybody who hasn't realised how unreliable human senses are and how easily  one is influenced  by external factors is a fool and shouldn't be trusted. 
  5. nick_charles Contributor

  6. regal


    No one is claiming magic,  science has many areas left not understood,  the brain being one of them, you think science has explained consciensioness and perception?  Calling people fools over the matter just shows a lack of background in the subject at hand..
  7. regal


    Nick you know better than that.   There is no working model of an FFT THD plot in correlation to the perception of hearing.   Until that code is broken, meter men are just pissing in the wind.
  8. nick_charles Contributor


    You appear to keep flipping between neuroscience and psychophysics, if you are referring to the underlying neurological mechanisms, I have mentioned that we do not need that level of detail, we have observable behavior and that will tell us adequately whether a person can detect such and such a level and pattern of THD. How it works is interesting but not necessary. We need only alter the THD and test subjects , this is not difficult. If you want to read studies of correlates between audio signals and neurological activity the rather controversial Oohashi paper is an interesting read.
    In the end we are interested in whether A is audibly different from B, how this relates to the underlying neurological mechanisms of perception is a different question. If A and B are (reliably) different then we can look into the underlying properties of A and B far more easily and more usefully then the workings of the brain.

  9. regal
    You are arguing for an empirical method that is far from scientific,  how do you do a guage R&R on a test subjects perception of hearing?
  10. nick_charles Contributor

    There are several meanings of the R&R acronym, which one are you referring to ?
    Since my approach is so unscientific, I'll ask you, how would you determine whether or not a person can *reliably* detect a difference between two components of the same type ?

  11. bigshot
    I think he uses a Oujii board.
  12. Bianci1969
    I've been reading Mr. Goodman's responses and boy are there some holes in his argument.
    In practice, Asynchronous does not offer a significantly easier or cheaper clean up experience. Our DAC is cheaper than some asynch implementations and yet is sounds better in many respects, so it's not about component cost.
    Mr. Goodman, Asynchronous doesn't clean up jitter. It prevents it from happening in the first place. This is an important distinction, one that you keep word-smithing around. You are correct though, it must not be easy. Otherwise, everyone would be doing it rather then purchasing OEM  adaptive solutions.
  13. mgoodman
    @  Bianci1969
    There is no wordsmithing. Asynchronous does not "prevent" jitter. It re-clocks it. There is a difference, which you can see by performing a simple experiment. Take an Asynchronous DAC. Put a jitter analyzer on its USB bus and you will see tons of jitter on the USB cable, coming in to the DAC. That's because samples always come in irregular bursts. Sometimes fewer, sometimes more. The Asynchronous DAC then cleans this up by buffering a certain amount of samples and then re-clocking them with a fixed oscillator. So on the input to the Asynch DAC, there is jitter, even though it controls the data rate coming in. On the output, there is no jitter.
    The same exact thing is happening with the better implementations of Adaptive. While the two approaches are obviously different under the hood, from the perspective of the data coming in and going out they behave similarly. When the data comes in from the computer, it comes in irregular bursts, the only way a computer knows how to send data to a peripheral device. If the Adaptive DAC can take those irregular batches of samples and "line them up" correctly (re-clock, based on a fixed clock oscillator), then what goes out of the DAC is also jitter-free.
    In both cases the data coming in has jitter, the data going out does not. Asynchronous does not prevent jitter. It still faces jitter on the USB cable as samples come in and needs to clean it up by buffering and re-clocking. If you know how to clean up the jitter, you can do as good of a job with Adaptive. If you re-clock your data properly, it doesn't matter if you use Adaptive or Asynchronous. Both will effectively take a jittery signal on the USB cable and make it jitter-free at the DAC.
    Notice how I'm not arguing the point that "Adaptive is better". If I had a bias, I would state it. However here I don't have any bias for one simple reason. My argument is that neither approach is "better" than the other - if the engineer does his job right, the results will be the same.
    If the engineer does a poor job, well, then all bets are off, no matter which technology you use.
  14. regal

    Guage R&R is the basis,  the foundation of any empricial scientific study: http://en.wikipedia.org/wiki/ANOVA_Gauge_R%26R 
    I don't think you could create a humane scientific study to reliably determine differences in human perception of music. 
    Its been a good discussion,  you are certainly well read and rational but I think our public conversation is exciting the less educated into immature low blows and name calling,  so I think we both should take some time to contemplate each side of the argument and perhaps continue the discussion over PM..

  15. regal

    Mr Goodman, You are confusing asynchronous USB protocol with asynchronous reclocking.   The asynchronous USB has no reclocking,  it simply means the USB device holds the master clock instead of the computer (adaptive).

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