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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. Bmac

    Quote:

    Really? So all the synchronous DAC's in the world don't work with CD audio? That's news to me (and probably several DAC manufacturers and their thousands of clients).
     
  2. Bmac


    Quote:
    In response to point 1: I wasn't quoting the numbers to prove audible superiority, and I don't think that was implied either. For $2,500 I would fully expect your DAC to sound subjectively better than a $400 competitor. I was however quoting Stereophile's numbers because they are the only published jitter measurements that I know of that are third party, reasonably reliable and which contain at least a few of both types of USB DAC's. Yes the measurement hardware will change over time, but I believe all the DAC's I mentioned were measured within a short period of time using the same gear. So I submit that the Stereophile measurements still have some validity with regard to jitter until something more reliable is available.
     
    In response to point 2: I never said that "good enough" was good enough. Building products that are technically better is an admirable pursuit. Having said that, I haven't actually seen any proof yet that well-engineered asynchronous DAC's in general have lower jitter at the analog outputs than well engineered synchronous DAC's. But assuming they do have lower jitter, the other problem is that again there is no proof that a product with 50ps of jitter can be discerned by human ears from a product with 120ps of jitter. I don't think they can. The asynch camp has been very vocal about the fact that their products sound better because they have lower jitter. That seems to be the only claim for audible superiority. I think the onus lies on the proponents who are very vocal about their superiority to prove that their products are in fact technically superior, and then that the technical superiority is actually audible by human ears. Neither of those criteria has been satisfied yet.
     
    In response to 3: I'm not an engineer, so I won't attempt to dispute the point that all other things being equal that asynchronous will have lower jitter than synchronous. It very well may be fact. Having said that though, there are an infinite number of ways and parts to design a DAC with so in the real world all other things are probably never equal. Every DAC takes it's own approach; what matters is the end result. From what I've seen anyway, synchronous DAC's can be just as capable of low- jitter output as asynchronous.
     
  3. nick_charles Contributor


    Quote:
     
  4. Bianci1969
    Hello Bmac-
     
    To quote the Well Tempered Computer..."

    Synchronous

    The clock is directly derived from the 1 kHz frame rate. There is a PLL that takes in the start of frame signal and generates a clock. Using this scheme its rather difficult to generate 44.1, but very easy to generate 48 kHz. This is a primary reason why many early USB audio devices only supports 48 kHz, they used this mode"
     
    I guess it's not impossible, but impractical. If you could, tell me what USB dac's are running synchronous usb at 44.1khz. I'm not aware of any.
     
    Bianci
     
  5. Bmac
    I'm not really sure what you're getting at. I've never heard of a USB DAC that didn't work with CD quality audio. Here's one that explicity supports 44.1 over USB and costs a whopping $99. It must be very difficult to do. Maybe designers need to throw lots of money at this problem to get good results too! [​IMG]
     
    http://www.nuforce.com/hp/products/iconudac2hp/
     
  6. Bianci1969
     
    if you divide 12MHz by 44.1kHz you get 11.2896...MHz. So why bother using synchronous when the clock rate vs the standard sampling rate of 44.1kHz are not mathematically compatible? 48Khz is nice and tidy for synchronous but why bother implementing this format if 99.999999999999999999999999999999999% of all music sold is 44.1?
     
    I didn't see any mention of what type of USB interface Nuforce uses on this piece. But if the measurements from a recent CD player review are any indication of their engineering abilities I'll pass...
     
    "This is one of the highest levels of jitter I have measured, and about 20 times higher than in the best products I have measured." - Atkinson
     
    http://stereophile.com/content/nuforce-cdp-8-cd-player-measurements
     
  7. nick_charles Contributor


    Quote:

    that is a lot of jitter...and yet the listening reviewer thought it was a good CD player, either it is another one of Stereophile's many deaf reviewers or ...perhaps jitter just does not make that much diffference ?
     
     
  8. HeadphoneAddict Contributor






    I have a CDP-8 which sounds better than my Apoge mini-DAC. Nuforce found the cause of the jitter and fixed it for future shipments, and offers the fix to current owners. I'll send mine in for the update; but apparently low frequency jitter is harder to hear and doesn't wreck the sound. Everyone who heard mine at RMAF was impressed with it.
     
  9. mgoodman
    @ CHanson,
     
    Chris - You need to stop accusing me of falsehood and instead re-read your own argument: "(if all else is equal) that an asynchronous DAC will have lower jitter than an adaptive DAC".
     
    1) What specifically is the "Else" that's being equal? Consider that the "Else" in our Adaptive circuits keeps winning industry recognition, magazine awards and customer satisfaction. "All else being equal" is a theoretical argument that's disconnected from reality.
     
    2) It's not enough to say that "in theory" your approach is better. Everyone on this forum knows that we don't live in a world of theory. We live in a real world, where practical design is what makes or breaks the product. Put a bad clock in your Asynchronous implementation and you've just made the worst DAC ever, despite using your "theoretically correct" approach.
     
    So let's stop hiding behind purely theoretical arguments - they don't get you anywhere. Let's get practical and focus instead on making the best products we can make.
     
  10. regal
    An abacus can do addition and substraction,  in theory a calculator can do the same with better speed and accuracy.  Yet the abacus makers didn't have the programmers and engineers with the know how to make calculators,  so they went out of business.   Why don't you hire a few software engineers and develop an asynchronous protocol to at least compare to your mighty adaptive devices,  companies that don't explore new developments typically don't last long.
     
  11. Bianci1969
    Mr. Goodman,
     
    I guess the question is this-. what implementation is better, Asynchronous or Adaptive? If you could figure out the code to Asynchronous would you be using it? If Gordon Rankin or DCS were offering you a license would you take it? Or, do you stand behind Adaptive as a superior method for transferring audio over USB?
     
    Bianci
     
  12. Bmac

    Quote:
     
    Is this a serious question or just bad trolling?

    Quote:
    Bianci, you are aware that the synchronous USB protocol that Mr. Goodman developed for Centrance is licensed to other manufacturers and is used in some well respected (and measuring) DAC's, right?
     
  13. audioengr
     
    Quote:
     
    This is like so many reviews.  You dont know the quality of the reviewers system.  Listing the components tell you nothing really.  The only way to know is to be there and play a sample track.  They typically dont do shootouts so you dont know what they are comparing it to.  Some online reviewers that dont care about stepping on toes actually do shootouts.  I like these guys because I'm not afraid of losing.
     
    There are dozens of preamps out there that create so much noise and distortion that any benefits of lower jitter are lost in the noise.  Jitter can also be euphonic, like "tubiness", having a masking effect on other system nasties, actually a positive thing.  This is definitely going down the garden path however.....
     
    The reviewers are not deaf, but their systems are sometimes crippled IME.
     
    Steve N.
    Empirical Audio
     
  14. audioengr
     
    Quote:
     
    You need to check your math.  If you divide 11.2896MHz by 256 you get 44.1kHz.  In Async systems multiples of 44.1 and 48 are used for the two clocks.  Even multiples.
     
    In one CEntrance Adaptive interface a 6MHz clock is multiplied up to 48MHz.  This is then used to synthesize all of the sample-rate frequencies.  You can easily look this up in the datasheets.
     
    Steve N.
    Empirical Audio
     
  15. bigshot






    Do you happen to have a citation on that? Thanks.
     
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