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MDAC First Listen (Part 00101001)

Discussion in 'audio' started by JohnW, Aug 12, 2015.

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  1. misterdog

    misterdog Not the canine kind

    My wrong, all digital is based on 0/1 so all must be equal, and perfect. :)
     
  2. rtrt

    rtrt pfm Member

    Hi John do you plan to continue with the MDAC mix of both XLR and RCA output connectivity? Ive found it useful, though I do appreciate that converter cables are available :)
     
  3. BE718

    BE718 pfm Member

    Then with respect you are doing something wrong or have some problem with your setup.
     
  4. BE718

    BE718 pfm Member

    So why do , probably literally millions of people use untweaked PCs without issue? I dont think its the computer with the problem.....
     
  5. BE718

    BE718 pfm Member

    Great stuff John,

    So my question is what is happening in the MDAC when it receives the data.

    Can you explain the process - does the decoded audio data end up in a buffer and clocked out locally? So is the USB packet jitter causing effects through modulating supplies, ground planes etc?
     
  6. JohnW

    JohnW Trade: Lakewest

    Yes the RCA output will still be available, but without the Current Sense feedback obviously :)
     
  7. JohnW

    JohnW Trade: Lakewest

    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.

    So I dug up a Digital scope - rearranged the lab to make space for it... I think its the first time I've really used it - I hate them, but it proved useful to capture the data.

    https://dl.dropboxusercontent.com/u/86116171/direct usb.jpg

    Above is a colour graded eye pattern of the Direct PC USB connection to an XMOS based DAC (streaming 1KHz, 0dB FS) High speed USB.

    Note the multitude of lines, but more importantly that the background is not black (Black means no data points fell in this area) - the background its dark blue because during the acquisition low frequency "Runt" waveforms where sampled in this area - these "Runt"waveforms occurred as the PC / operating system processed other applications / Operating system house keeping tasks etc. On the Analogue scope it was a horrific mess...

    https://dl.dropboxusercontent.com/u/86116171/regen usb.jpg

    Now with the ReGen USB Data, notice not only the much cleaner waveform but far more importantly that there is very little "Runt" data - the background is Black. The USB Hub IC in the Regen has for the most part cleanly repackaged the data.

    The colour grade data sample hit size is the same for both plots (20K Hits on the Red).
     
  8. JohnW

    JohnW Trade: Lakewest

    Yes, I strongly believe that the USB Packet jitter cause "second order" effects in the MDAC (PSU, Ground plane and RF modulation).

    I realise that the MDAC's USB device (the TAS1020B) not only decodes the USB, but its also the house keeping processor on the MDAC mainboard - so its directly connected to the ESS DAC (via the ESS's I2C MCU configuration port) allowing multiple RF coupling paths between the external USB Host device (PC / Computer) and the ESS DAC.
     
  9. sbgk

    sbgk pfm Member

    bit of an assumption to say that software players and computers affect sound quality, my objectivist friends say that sound engineering principles and measurements says that they all sound the same and no dbt has proven otherwise. All very confusing, especially as I do hear differences.
     
  10. avole

    avole He who can, does. He who cannot, teaches.

    All of which explains why wireless or optical is the way to go. Oh, and why there's no difference between USB cables, which can't act as filters.
     
  11. LarsS

    LarsS pfm Member

    Done some listening evaluation of Regen and AQ Jitterbug in my system this weekend.

    Using Roon (go try it if you haven't already) as player, overspecified MediaPC w. PPA v2 USB card (HDPlex LPS) - AQ JB - Regen (HDPlex LPS) - Norma Internal DAC.

    Listening on my goto evaluation CD-rip "The All Star Percussion Ensemble". Improvement noticed when I added Regen in my system, no improvement noticed when adding the AQ JB.
     
  12. Bob L

    Bob L pfm Member

    John,

    Even though I don't really understand what I'm looking at, the difference is so spectacular that I have to wonder if you have quietly taken a job as a sales rep for Uptone Audio!

    It is very clear from these that what is going to the DAC is drastically different in the two cases. I know it's a long stretch from the pictures to be able to say that this is a difference which we can hear, but at least it correlates well (even to the 'blackness' which some people report for the sound with Regen....). You don't say anything about PS, so I assume this is with the SMPS, and I'm quite anxious to see what comes from using a linear supply. Nevertheless this is a clear demonstration, probably the first one, that the Regen really does do something measurable to the data.
     
  13. ti33er

    ti33er pfm Member

    hmmmm isn't it time that someone invented something revolutionary with all these sub-optimal data transfer mediums that we use - perhaps a true TxRx fibre optical connection port for audio equipment, that isolate electronics by default and are incredibly accurate?

    'Someone' please invent a new Industry standard :) ...come on Mr John, I am sure there are a number of us that would back you...after the FDAC and VFET before I get shot!!! ;-)
     
  14. Rune

    Rune pfm Member

    John is working on it it and it is called the Detox;)
     
  15. adamdea

    adamdea pfm Member

    John -thanks this is very interesting.
    I'm not 100% sure what I'm looking at, could you help me to understand- is this in effect the plot of many many cycles of usb signal (voltage against time) overlaid ?

    If it is then I can see that the main signal (high crossing to low and back again forming an x) is much sharper in the second case, showing much less fluctuation from one cycle to the next.

    Also I see the difference in the background colour which I understand forms some sort of spuria. I also see that there are 3 green horizontal lines on the non-regen version - what are these (are they the rest state of the signal between data?)

    I'm trying to understand how we should interpret this information. I suppose it's difficult to be too prescriptive here because it's not clear what the transmission mechanism is for whatever undesirable results we are trying to eliminate
    1) the signal shape itself on the basis that it somehow directly affects the dac however it is read (as in your example of the jitter on the signal which somehow radiates within the dac even when the data is fed into a buffer via (in my words not yours) the glitch caused each time data is read into a buffer)
    2) the signal shape insofar as it causes the usb receiver to have to try hard to read the data (this is what I understand to be JS' hypothesis)
    3 the noise in the signal (not the 5v line) which somehow pollutes the dac through some other mechanism
    [have I got this right- are there other mechanisms I have missed]
    4) the noise on the 5v line (not not relevant to this plot I assume)

    Having regard to those considerations (particularly the first and second). I'm trying to get my mind round the question of what it is about the signal that really matters. Am I right in thinking that because usb is a differential signal the receiver would automatically ignore the common mode noise, as it would be reading the difference signal? If so wouldn't it be the difference signal which mattered for mechanism 1) and 2)? If so would there be any way of showing what the difference signal looks like. I'm not sure how much of the pre-regen noise would disappear.

    Also how exactly does the receiver read the data: is it as a single transition from high to low or low to high to indicate a change in bit value or does is read more than one change to encode a change in bit value (as IIRC S/PDIF does). From the point of view of how hard the receiver has to try to read the signal (mechanism 2), it still seems to me that the pre-regen signal might be "good enough".

    Apologies for the rambling, I'm just trying to work out what this all means.
     
  16. adamdea

    adamdea pfm Member

    I don't want to seem pedantic but it does not show that - it shows that it does something to the signal which carries the data. I would expect that (to some extent) of any change of transmitter. It's true though that the change seems to be beneficial (unlike that on the jitterbug measurement from Paul Miller) in a general way. It also looks like a big change I agree.

    The question is what is a significant change in this context. The conventional theory is that many changes are irrelevant; that's why digital signals exist. The data is almost certainly going to be read with 100% accuracy either way. Given that we are talking about asynch usb, jitter is supposed to be irrelevant. On the face of it the conversion clock will be unaffected by any jitter in the datastream. That said I understand that there are various theories as to how it might be indirectly affected or the jitter might get to the analogue output by another route.

    This is not to say that John's measurements are not interesting, but they are a small step.

    As regards SMPS vs linear. I would not expect them to make much difference to this plot of the signal (as opposed to the power line) but I'd be interested to see.
     
  17. peperoni

    peperoni Officially now an Old Git

    The point is surely that esoteric cable sales and foo regeneration is dead in the water if everyone realises that a systems that only sees 0 and 1 or on and off does not care about all the mush in the middle.
     
  18. Bob L

    Bob L pfm Member

    I agree entirely- very sloppy language on my part. However, it is of course the signal, not the data, which the DAC has to struggle with.

    Bob
     
  19. Purité Audio

    Purité Audio Trade: Purite Audio

    Adam have you read Julian Dunn's 'Jitter Theory' it is really interesting, Alan sent me the PDF, if you haven't I will email you the document.
    Keith.
     
  20. adamdea

    adamdea pfm Member

    It is, but does it struggle? That's the point.
     
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