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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






    Very likely. Auditory masking can occur with imbalances as small as 3dB. The effect isn't just at the location in the frequency spectrum it occurs. It can affect the frequency an octave up as well. If you get a few of these in the wrong spots, it can really mess up your sound. It doesn't matter as much with electronic music, but for orchestral and acoustic music, a carefully balanced response is very important.
     
  2. regal


    Quote:


    You are the one with all the answers,  all I can tell you is I have 4 transports and each one sounds different.  No one has mapped the human hearing perception neural network as far as I know there are many mysteries to be uncovered.  
     
  3. Dynobot


    Quote:

    I take it you have not taken any steps to acoustically treat your room.
     
    Do you use a professional room correction software/hardware or do you fix the imbalances by ear with an EQ?
     
    I have seen a few people with audio set-ups in the $20K range who swear by VST plugins to fix their sound, in my opinion if you spend $20K on a sound system and it still sounds un-listenable then there is something fundamentally wrong with the synergy in your gear and/or room.
     
    You made a comment about a forum where people talk about techniques....kindly share your technique, which VST, room correction, and or eq product.
     
    Thanks in advance.
     
  4. nick_charles Contributor


    Quote:


     
    Hello Steve, long time no see, been in prison ?
     
    Steve, you are being a little bit disengenuous here. You know full well that there are different variations of jitter and only signal-correlated jitter has been empirically tested to be detected at levels of about 20ns (Benjamin and Gannon) in music which is 100x the level of that found in a competent DAC (200ps) or 10ns as pure tones at 17K, random jitter however has been empirically tested to be undetectable at up to 250ns (Ashihara et al) which is 1250x worse than a competent DAC, please get your facts right [​IMG]
     
     
  5. nick_charles Contributor
    If you have a good quality ADC a worthwhile experiment is to record the analog outputs from your DAC using each of your 4 transports. With my setup I found slight differences between using the optical and coax inputs on my DAC (with the same transport) , but you can map the FRs of your transport/DAC combos so if differences exist they can be reliably compared and quantified. That said I do have a transport that is verifiably not bit-perfect (adds gain bizarrely)  but it is a low end streamer.

     
    Quote:
     
  6. Syan25
    Ethically speaking - the concept of using EQ is not sound. Though I understand the use for it in playback within the short-comings of a room, as a musician, we try to nail it in the recording - bringing the most authentic sonority of what we made.
     
    I would hate to know that some one is playing my recordings and using an EQ... I understand it's necessity but I have never liked the idea of it. It makes all our hard-work in the recording studio seem futile. It may be useful for old recordings though
     
    We also hope that people listening use the best  hi-fi or head gear possible to enjoy what we produce.
     
    As a listener - I do spend money on trying to get the best speaker/room requirements to enjoy listening at home. I also use headphone amps, cables and headphones that help me enjoy music.
     
    My ideal is to have balanced-neutral sound to keep sound of the original recording exactly as it is - and I try to avoid any kind of interference including low-jitter or anything else that may pop up.
    Good equipment lead to good results and sometimes we are lucky enough not to spend too much money get those results.
     
  7. Dynobot
    Its just an excuse for people who have the money to buy good gear but have no idea how to create a synergy between the components themselves and the room.  Like I always say, if you spend thousands of dollars for top notch gear and you still "need" to use an EQ in order to make your music listenable there is something fundamentally wrong with your setup.
     
    Quote:
     
  8. Syan25
    Absolutely right. Doesn't make any sense.
     
  9. Dynobot
    Furthermore if anyone has ever heard an acoustically FLAT room they would not like it. 
     
    People "Assume" that their ears will automagically like perfectly spec'd music, but such is not the same.  Tube owners of the world will tell you how they love the added even-order harmonic distortion that tubes give for example. 
     
     
  10. bigshot




    How much you wanna bet that these guys just looked at your numbers and glazed over and assumed that your post corroborated their misconception about the audibility of jitter?

    I find it's easier to just cut to the chase and say jitter is not something to worry about. If they want to verify that, they've got the citations. If they don't, I will feel free to have fun speaking over their heads to you.

    I love the argument that we wouldn't like flat frequency response if we heard it. I hear flat response every day in the sound around me in the real world. It wouldn't sound better to me if I had a filter on my ears coloring the sound to the way an unbalanced stereo presents it. There's some high grade absurdity being dished out here!
     
  11. bigshot
    P.S. Tubes are a hoodoo too. There was a study where an ordinary solid state amp was filtered to color the sound to match a high end tube amp. Audiophiles couldn't tell the difference between the two. Lookitup, my man!

    This may come as a shock to you, but inaudible levels of harmonic distortion sound better than even order harmonic distortion and inaudible levels of jitter are... well, inaudible!.
     
  12. Dynobot


    Quote:

    Just were do you live?  In a anechoic chamber?  In my world I hear reflections all the time.
    If I spoke to you in my living room for example, and the sound was measured, you would find all sorts of reflections due to the room acoustics being poor.  If I played a base guitar in two acoustically different rooms you bet it would sound different.
     
    So do you want to take sound as it is presented to you irregardless of the room and call it pure?
     
    -or-
     
    Do you want to EQ everything to taste and call it pure?
     
    Can't have both....get off the fence!
     
    Myself, I treat the room properly and take the sound as it is presented...without EQ flavoring thank you.
     
  13. Dynobot


    Quote:


    Yeah Bob Carver did that, don't have to look it up, I read it in real time after it happened.
     
  14. bigshot
    EQ doesn't just correct for room acoustics. It also balances out the response of transducers. Balancing the frequency response of a stereo in your living room is not the same as being in an anechoic chamber. When you listen to acoustic instruments, it is important to have a balanced response because we as humans know what a violin sounds like. Whether we put the violin in your living room or mine, it still has an unique response. In order for it to sound natural, it has to be presented with a natural balance. This is particularly important with the complex harmonics of acoustic instruments because first level harmonics intersect with the same frequency that auditory masking can mess up.

    I had a friend demonstrate this vividly for me. He played a recording of an acoustic guitar and boosted a midrange frequency by just a few dB. I couldn't hear a difference in the midrange, but suddenly the higher frequency seemed muffled. The boost in the mid was affecting the harmonic in the upper range. I never would have believed it was so big a difference if I hadn't heard it for myself.
     
  15. CHansen
    Quote:


    I strongly agree with the first and third paragraphs that Mr. Goodman wrote.
     
    However the second paragraph is simply incorrect (somewhat ironic given the content of the third paragraph). The truth is that, if all else is equal, it is absolutely impossible to build a variable-frequency clock (as used in an adaptive mode USB DAC) with as low a jitter level as a fixed-frequency clock (as used in an asynchronous mode USB DAC).
     
    Generally speaking, the more money you throw at a technology, the higher the performance you can achieve. And 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.
     
    Sure, it is possible to make a really good variable-frequency clock that has lower jitter than a fixed-frequency clock. But only by spending a great deal more money or if the fixed-frequency clock is an extremely poor design. Engineers have worked for decades to reduce the jitter of variable-frequency clocks. High-performance ones tend to be complex and expensive. In the meantime, fixed-frequency clocks are simple to design and build. Even the simplest, most inexpensive fixed frequency clock will have lower jitter than an excellent variable-frequency clock as long as you feed it with a nice quiet power supply.
     
    As Mr. Goodman pointed out in the first paragraph, the incoming USB signal has high levels of jitter. A typical adaptive clocking scheme is to use a PLL, which will filter out some of the jitter. More sophisticated (and complex and expensive) systems will use two PLLs to achieve higher levels of jitter filtering. But with asynchronous, the incoming jitter on the USB line is completely immaterial. The only thing that matters is the quality of the fixed-frequency clock, which as noted previously is practically a trivial thing to design.
     
    I would be happy to compare phase-noise plots of our fixed-frequency clock with Mr. Goodman's variable-frequency clock any time. (A phase noise plot is the most sensitive way to measure the jitter of a high-frequency clock.)
     
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