DoP isn't PCM

March 19, 2014
 by Paul McGowan

Ok, there's just too many TLAs going around here (Three Letter Acronyms). Engineers are obsessed with them because it makes for quicker communication of complex terms, and that makes sense, but what's a poor Audiophile to do?

Recently I have been getting a lot of email questions about DoP (DSD over PCM) and most of the questions would suggest folks aren't understanding what DoP is. In fact, much of the mail I have been getting suggests folks think DoP is converting DSD to PCM (there's those pesky TLAs again). And the question that generally come from that partial misunderstanding is "I don't want to convert pure DSD to PCM, it'll change the way it sounds". Right. Wrong.

Right that converting DSD to PCM changes the sound; and there's a group of folks that find DSD downsampled to PCM sounds better than DSD (as illogical as that sounds). I have personally heard examples of this "betterment" and while I too hear the improvements, I remain unconvinced this is anything but an anomaly we need to figure out. And then there's DirectStream that converts PCM to DSD and definitely sounds better for it. It's all so confusing.

Wrong that DoP has been converted to PCM and that it will sound different than DSD; it isn't and doesn't.

Tomorrow, let's take our time and get to know DoP a little better and gain an understanding of how it works and what's going on.

See you tomorrow.

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15 comments on “DoP isn't PCM”

  1. I look forward to this topic Paul. It's kinda Greek to me. I do it with jriver . As one of the dacs I have does use this format . As it cannot stream dsd128 only 64 . So dsd 128 I must use the USB input and that is the way it works.
    And the unit indicates it's 24/176 when playing it . So I am way confused in this too.

    Thanks
    Al

    1. I look forward to this topic Paul. It’s kinda Greek to me.

      Me too Al, but you probably meant GEEK, not Greek. Which reminds me of an incident on an Aegean cruise, island hopping, when my wife, left alone in the cabin, took a shower.

      A steward accidentally walked in on her while she was in the shower. And left. Or I don't really know what happened. Or I don't care. Or whatever.

      Anyway she came down for breakfast and at the table told me: "I just need to tell you that while I was in the shower naked a GREEK GOD walked in on me."

      I told her "I just need to tell you, he was no Greek god, he was just a fucking Greek."

      1. Andrew that is really funny. It reminds me of a cruise I did at the very end of my first wife. 6 k on a cruise to Bermuda great weather . No life left between us, that was about 16 years ago. I could not wait to get back 7 days
        And yes for me I could not care who did what or when. Funny though , did you buy. A kit ?

        Al

        1. No Al, didn't have to. My wife to the best of my knowledge was not the football in the locker room. She despises people who cheat in any manner or form and leaves big tips. Not leaving a tip is cheating in her mind.

          She worries about me for good reasons far more than I would about her. I was always a bad boy. Quiet, but bad. She's very shy, conservative, gorgeous, and very headstrong. Like my mom. You know how it is, my mom taught me how to debate, quite well I think, and I never won a debate with her. Not f$%^&ng once!

          1. Great reply. and I happy for you . Much cheaper to keep them too. But all joking aside I am glad to see people get along.
            The one I have now is the right one even at my age and having a 7 year old. It's all good.

            Al

  2. Bits is bits - in the transmission and storage chain. I don't think it makes much difference how your remember your digital samples - encoded as PCM or encoded as DSD or Apple Lossless or....

    Nor should converting between these matter - as long as one doesn't encounter numeric problems like overflow - because such format conversions don't affect the data. If you can 'round-trip' a conversion - say PCM to DSD to PCM - and recover the same bits, the data's unchanged.

    What does matter a great deal is the A/D and D/A converters used. The A/D is largely out of our control (for purchased digital music), but that leaves the D/A.

    Pure single-bit D/A should sound better than any multi bit if only because there's exactly one voltage (or current) source to hold perfect.

    So the DAC matters, but not the storage, transmission etc.

    Theory is wonderful, eh?

    -- P

  3. Hi Pete, you say 'So the DAC matters, but not the storage, transmission etc.'

    I've had a pair of Lyngdorf TDAi2200 amps in my system for many years now, they are DACs. I've had various iterations of source (e.g. Denon, oppo, Mark Levinson CD and many PCs). The TDAs only accept a digital input, XLR has remained my standard carrier ever since I bought them.

    Do you include software in your 'transmission', because there are clear differences between the programmes I've used (e.g. WMC, XXHighend, JRiver) and between system modifiers (for want of a better term e.g. JPlay, Fidelizer, Audiophile Optimiser). I'm currently using Windows Server with no GUI as opposed to the XP/7/8 I have used.

    Those are the soft components; I've replaced the PC PSUs with Linear PSUs. The 'storage' HDDs replaced with with SSDs. I use separate SSDs for OS and music and so on. Good SATA cables and shielded DC lines inside the PCs were a revelation. I'm using a P5 in front of the LPSs (and TDAs) and my PCs are on PowerBases, all physical changes before the DACs.

    All the while my DACs have remained exactly the same - but there has been a massive improvement in the sound quality I'm getting; all contributed to by the above changes to 'storage and transmission'

    Hence your statement caused a raised eyebrow here
    regards
    Andy

  4. It all matters but it varies with different dacs.
    Cheaper dacs it matters far more thAn much more expensive ones. And this is easy to hear
    As good as the pwd mkii is the obvious improvements with changes in the chain matter. As I use an offramp to archive it's best.
    But I do have. Couple of other dacs not so much. Bu what really matters is how much we need to find out. As this is what I do not have. As the new DAC will work with all setups much better and less playing this is far more important than a SS or spin drive
    Al

  5. So are we talking about a synerio where we have PCM converted to DSD which removes noise bits and then it gets converted back to PCM minus the noise?

  6. If I covert an MP3 to AIFF, how can that be ?
    I assume an MP3 is 10% and an AIFF is equal to 100%, how can you make a better file if you start with less information ?...

  7. On another matter raised by Paul somewhere else, observing that his new DAC design plays back CDs so much better than the norm, somewhat diminishing the differences between it and hi rez, it is a matter I've been aware of, but could not voice.

    Very few DACs can accomplish what Paul observed, and considering that 95+% of the libraries we own, and will continue to own, better CD playback may be just as, if not more, important than playing back 192k or DSD.

    So in my comparisons of relatively few DACs, I must have wound up preferring the DAC that played back CD's better! It separated the men from the boys.

    1. Thanks Andy. One of the more intriguing characteristics of this new DAC is, indeed, it's ability to render all the details buried in the CDs. The more I listen to this DAC, the more I listen to CDs. I thought it would be different. Yes, I thought with this DAC I'd be surrounded by oodles of DSD and high rez materials but, in fact, I am increasing my enjoyment of plain old redbook and really enjoying the revelations of just how much is buried on those discs.

      One of my favorites is a 1959 recording, on analog tape of course, remastered to CD expertly by someone of Buddy Holly singing True Love Ways. It's the first or second track I'll play for people interested in hearing the system. You'd think I'd play a DSD, but no, it's CDs that rule right now.

      Go figure!

  8. Andy Stoneman

    I reckon that if the bits is different, the music will sound different. I suspect that Pure Music (for example) provides different bits than iTunes.May just be the 'theoretically below the noise' bottom 4 bits (on a 24 bit system) which mayhap the software recomputes because it thinks it knows better what the dither should be.But if you have the same bits, what matters is the DAC.

    And yes, using power amp DACs is likely to sound different from 'classical DAC into class A/B amp' - different DAC, and different conversion process (if I recall correctly, self-oscillating as a result of a comparison feedback loop rather than combo ladder DAC/delta-sigma as Burr Brown etc might use)

    Luckily, I'm no expert at all on Windows audio, but it has always seemed to be for too bloody complicated, with driver upon driver getting in the way and doing weird sh*t to the bits. So if you're using Windows, your mileage may not only vary, but vary unpredictably and perhaps uncontrollable. Buy a Mac Mini (not for computing, I respect other people's religions) but just for iTunes/Pure Music or whatever.

    -- P

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