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Thread: Science Thread: Review of Audioquest Jitterbug and Uptone Regen USB Conditioners

  1. #21
    Quote Originally Posted by amirm View Post
    I came to post what he had written here and you saved me the typing .

    I don't know what the heck that is but this is not what I expect the eye pattern to be on a USB port with a short cable. I can't imagine the above eye pattern being from a USB compliant port.

    There is unfortunately no USB police to speak of so it is entirely possible for him to have an implementation that is not well implemented.

    Anyway, even if we are going to talk about eye patterns, we better show a broader spectrum of USB ports than one unknown one here.
    Ah ha... Of course... It was the old non compliant unknown USB port trick again...

  2. #22
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    Quote Originally Posted by amirm View Post
    Then I read the initial line that he is using some kind of "heavy "CPU Process" jitter modulation?" I don't know what the heck that is but this is not what I expect the eye pattern to be on a USB port with a short cable. I can't imagine the above eye pattern being from a USB compliant port.
    Amir, whred did you read about those "heavy "CPU Process" jitter modulation" ? I have read this thread closely (I highly recommend to anyone interested in digital audio) and I didn't get an impression he was using anything else than a regular computer, like we all do.

    http://www.pinkfishmedia.net/forum/s...176975&page=62

    Rather than posting assumptions about USB ports beeing out of spec etc., I would rather see more detailed measurements beeing posted. We can speculate all day long about many things, but that will not bring us closer to understanding the nature of those problems. John Westlake is working on a competing product, so he certainly hasd no interest in making Regen look better than it realy is. Plus, if you see all the equimpment he has (including megabuck phase noise analysers) - he is definately one of the very few people in this field who know what they are talking about.
    Adam

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  3. #23
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    Quote Originally Posted by Elberoth View Post
    Amir, whred did you read about those "heavy "CPU Process" jitter modulation" ? I have read this thread closely (I highly recommend to anyone interested in digital audio) and I didn't get an impression he was using anything else than a regular computer, like we all do.
    Oh, there is no such thing. There can be USB implementations that range from awful to great. As I said there is no USB police and typical PC use of USB is not very critical so if it works, folks often ship it. Now, if you bought a PC from Apple, HP and such, then I do expect it to be good and compliant. But on a no-name PC, random motherboard you built a server from, who knows.

    On the "jitter modulation" bit, it was in his post that you also quoted here:

    "The Analogue scope measurements of the USB direct and ReGen USB revealed the truly "horrid" nature of the USB traffic from a PC with heavy "CPU Process" jitter modulation - and I've been trying to think how to graphically capture it so I can post it here on PFM."


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    Quote Originally Posted by Elberoth View Post
    Rather than posting assumptions about USB ports beeing out of spec etc., I would rather see more detailed measurements beeing posted. We can speculate all day long about many things, but that will not bring us closer to understanding the nature of those problems. John Westlake is working on a competing product, so he certainly hasd no interest in making Regen look better than it realy is. Plus, if you see all the equimpment he has (including megabuck phase noise analysers) - he is definately one of the very few people in this field who know what they are talking about.
    I am sorry but I am not familiar with him. If he is a digital designer, then I can see him focusing on what he is doing. My expertise in understanding the full system and how to tease out audio performance. Focusing on eye pattern here is completely wrong. It has to be shown that the eye pattern matters on an asynch USB DAC and that has not been shown. An async USB has its own clock so as long as the eye pattern is good enough to extract the data, and you would know it with clicks and pops if it were not, we are golden. You can scrub the input USB pulses as much as you want and it won't make a difference to clock jitter directly.

    Yes, there can an indirect effect but if there is, we need to show that in the output of the DAC, not input before it even gets to the thing.

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    Thanks Amir, It's so good to hear a voice of reason.
    Sal

  6. #26
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    The guy is a renowed audio designer, both digital AND analog. That makes him kind of unique and surely let's him see the complete picture. He has been designing CDPs and DACs for the past 25 years or so. Many of his designs won varius 'Component of the year Awards' from varius publications.

    As i said - I would like to see someone repeating your measurements on greater number of compononts, with both SMPS and linear one.
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    I always said that I would wait to see these measurements before I posted on this forum again & what I see doesn't surprise me, I'm sorry to say

    Amir, the extra spurs that you see in the analogue output after the Regen is inserted is the 8Khz noise from USB 2.0 microframe timing - something that was spoken of already & I believe is referenced by John Westlake & shown in his plots of with/without SMPS. Why this only shows with the Regen, I'm not sure but it might be that the signal timing coming out of the Regen is more accurate whereas the ordinary USB signal is operating much like a spread spectrum clock

    The "heavy "CPU Process" jitter modulation" spoken of by John Westlake is the fact that he sees significant low frequency modulation riding on the USB signal waveform - this LF noise is correlated to CPU processing which is why he thought of videoing it to show it - it's dynamic & causes the so-called runt events that give rise to the blue hue of the eye pattern.

    He is awaiting delivery of a spectrum analyser that is capable of capturing significant information in the analogue outs of the USB DAC.

    Frankly, I'm disappointed at the level of analysis & comment here & it confirmed my worst suspicions!
    Last edited by jkeny; 09-29-2015 at 01:34 AM.
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    Quote Originally Posted by BobShermanEsq View Post
    Ah ha... Of course... It was the old non compliant unknown USB port trick again...
    First welcome to the forum .

    Second, what would you like me to say? This is Paul Miller's of HiFi news making a measurement of the eye pattern in his system with and without AQ:



    This is John's:


    Set aside the colors in John's as that is false coloring based on intensity of the graph. In Paul's measurements the eye is completely clear, with or without AQ. It is wide open too. Both of these are characteristics of a compliant USB port that is driving a short cable. John's measurements are nothing like that. As he says, it is pretty messed up eye pattern with lines through the eye. It makes no technical sense that his eye pattern is typical of what comes out of most computers. If so, and you connected a long cable to your printer, there would be hell to pay in potential data losses.

    Maybe John has it right and it is Paul who has it wrong and found the one clean USB port out there. But if I were you, I would not put my money on that . If I were managing a team of hardware engineers there is no way I would let them release a USB port with John's measurement on a short cable.

    Again, there are a ton of USB implementations out there, some of which could pick up the crosstalk that the CPU activity spits their way. In our application, i.e. audio playback, uses almost no CPU on a modern computer. So even if CPU activity causes such issues, it is not typical in our application. I would love to see John repeat his test but this time with just a media player running and playing some music. And at least try it on one other computer.

  9. #29
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    Quote Originally Posted by jkeny View Post
    Amir, the extra spurs that you see in the analogue output after the Regen is inserted is the 8Khz noise from USB 2.0 microframe timing - something that was spoken of already & I believe is referenced by John Westlake & shown in his plots of with/without SMPS.
    Microframes in USB 2.0 are indeed 125 microseconds which translates to 8 Khz as you say. However your analysis I am afraid is not correct. Here is the graph again:



    The jitter side bands are 4 Khz above and below our 12 Khz signal, not 8 Khz as you said. That means our jitter frequency is likewise 4 Khz, not 8 Khz.

    I would be surprised if John didn't know this simple math about jitter side bands and confused this timing with microframing of USB. And I don't know what power supply graphs have to do with framing of USB packet noise coming out of a DAC.

    In fairness to Uptone/REGEN, let's not put more on their plates without properly analyzing such things. This is a complicated system and doesn't let itself to quick and dirty guesses.

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    I like to emphasize something: the increased jitter I have shown with REGEN is completely inconsequential. It is way low at -115 db or so. There are worse offenders from the DAC itself. And those are not bad either from audibility point of view.

    So please let's not put practical blame at their feet on this ground. It is curious, yes. Should it be there if we are saying the device creates a cleaner USB signal, no. But from the end result point of view it is not material.

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