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Sound difference between two DAPs in a DAP>DAC>AMP Chain

Discussion in 'Sound Science' started by Dramlin, Apr 10, 2019.
  1. Dramlin
    I'm hoping someone can explain what I'm experiencing with two different DAP's, as it doesn't make any logical sense to me. There's obviously some process in the chain I'm not familiar with, so I'm hoping for some education here.

    I've been listening to music for a few months using a DAP outputted via USB to a DAC, then a line out to an AMP. The specifics are Shanling M0 (DAP) > ifi nano BL via usb (DAC) > Cayin C5 via 3.5mm line out (AMP). This combination sounds fantastic, but my DAP (Shanling M0) crashes a lot, and I was looking for a better overall user interface. I purchased a fiio M6 and started comparing the UI and everything else. At the end of my comparisons I plugged in the M6 into my normal chain (m6 > ifi nano bl > cayin C5), and was surprised & confused when the sound quality was different from what I was used to. I went back and forth between the Shanling M0 and Fiio M6 several times, and on several different days, and each time I heard an obvious difference in the sound quality. The Shanling M0 as the DAP has more details but a thinner sound, whereas the M6 has a fuller sound with more bass and much less detail.

    This makes no sense to me as I thought the DAP is just transferring a standard format digitally over USB to the DAC, so I wouldn't expect there to be any sound change between two different source DAPs. So, if the DAC, Amp, and cables are all identical in the chain, how is it possible to have ANY difference on the final sound? Are different DAP's sending different data over USB to a DAC?
  2. castleofargh Contributor
    to go about this in the right order, it would be nice to have a controlled experience of the audible difference. I don't know the magnitude of the difference you're feeling or how much is readily obvious(or in your head), but we've all been fooled and fooled ourselves many times over, so more than a sighted experience would help get over the "is the change really sound?", and move on to try and find out why.

    with that said, here are a few ideas of what could be different(with zero guaranty that it would be audible):
    - the DAPs have some DSP turned ON
    - at least one of the DAPs is having trouble with some format and that ends up audible. usually real issues of that type end up with failure to play the file, or crazy artifact noises/stutter, but I got one time(that I could notice and confirm objectively) where the format was playing as if everything was fine, but the sound was ... let's just say strange enough that I would notice.
    - USB has different modes of interaction, so depending on the DAP, a specific dialog is selected at the handshake when they fight to decide who's going to be king of the clock and ruler of packets.
    - maybe the DAC section is/can be fed by the 5V DC provided by the DAP(when the DAP provides it???), and one DAP just doesn't, or offers well below 5V resulting in the DAC not performing nominally?
    - maybe one of the DAPs oversamples the signal before sending it over and sucks at doing it, or does it just fine but then the DAC happens to have audible difference because of less than transparent filters at low sample rate?

    that's about as far as I can go to try and guess some causes for measurable differences. audibility is another matter and for most of the above, if things become readily audible, I would call that a problem.
    you could try to record both DAPs with a computer(if the soundcard's input isn't too crappy). something like RMAA can offer to check a few variables and would maybe help put a finger on at least the type of change that's going on. as for the cause, even with a few very superficial measurements, it's rarely easy to figure it out.
    Last edited: Apr 10, 2019
    Dramlin and TronII like this.
  3. bigshot
    Are you level matching the outputs and doing a direct A/B switched comparison? Before you decide there is a difference, you'll want to verify it with a quick line level matched, direct A/B switched, blind test. Then you can start thinking about why they are different.
    Last edited: Apr 10, 2019
    TronII likes this.
  4. overgang
    You're hearing things. All DAPs, DACs, and amps sound the same. Sound quality is defined only by extremities of the audio chain: the recording and the speaker (headphone).
  5. Steve999
    Perhaps that is an over-generalization. You’re perhaps far more right than wrong, but that level of generalization may hurt your credibility when you are trying to help someone to see things in a more accurate and sophisticated way. A truly reasoning person with limited knowledge might be justified in dismissing your opinion.
    Last edited: Apr 10, 2019
    buonassi likes this.
  6. Dramlin
    I am not. Since either DAP isn't able to control the volume (tested by trying to change the volume on the DAPs), I assumed, perhaps incorrectly, that the AMP volume would be identical between the two since I wasn't changing the amp volume in switching DAPs.

    While I don't have any great way of knowing for sure if it's in my head or which (if any) of the above items are the root cause, I'm just happy knowing that one of the above items could be the cause the for sound difference. I just couldn't think of any possible reason why two DAPs would sound different in the same chain, and now I have 4-5 possible reasons (at least).

    Thanks again everyone for all the replies.
  7. bigshot
    Line level output between components varies quite a bit. It's natural for lower volume levels to sound less percussive and more opaque and flat than louder levels. Differences of less than 1 dB are enough to distort comparisons. Even the exact same signal at a slightly different volume can sound quite different.

    The way you balance line levels is to run one or both of the outputs through a simple preamp with volume pot and level match. Then you run the lines into a switcher to do a switched comparison. The equipment to do quick controlled tests costs less than $50. It's very useful in cases like this, because it helps you eliminate the effects of bias and perceptual error. Then if there is a problem you can figure out where it is through a process of elimination. I do controlled comparisons whenever I buy a new piece of equipment to make sure it's audibly transparent.

    That depends if you want to just cut to the chase to resolve the question, or go through each of the steps of logic necessary to reach that resolution. The end result is exactly the same. We've talked about different kinds of pianos, technical issues of recording and playback like oversampling, power supplies and the peccadillos of USB, we've even dallied over into how pianos are tuned. But all of that is just lily gilding. it's pretty obvious that his bald summation, "you're hearing things" is the most correct answer we came up with. This is almost certainly perceptual error due to lack of controls. Nothing wrong with just pointing to the obvious and leaving it at that.

    I remember watching a young mother in a supermarket dealing with a tantrum. She was calmly asking the child why he was crying.... Do you hurt? NO! WAAAAA! Do you need something? NO! WAAAAA! Did someone hurt your feelings? NO! WAAAA!... These questions went on and on as she went through all of the reasons that the kid might be crying. It took forever! Eventually the kid became bored and had gotten enough attention so he stopped crying... much to the relief of everyone within earshot who had to witness this excruciating process. The mother accomplished her goal and crossed every T and dotted every i to Dr Spock standards, but the short and sweet of it was that the kid was acting like a little Schitt and a quick spank on the bottom would have solved the problem in a much less tedious and excruciating manner.
    Last edited: Apr 10, 2019
    Dramlin likes this.
  8. castleofargh Contributor
    I rejected the possibility of level difference because with the DAPS as digital sources, you could expect them to just decode to PCM/LPCM and send that for the external DAC, but I didn't consider the possibility of gain change as a precaution for EQ and other DSPs, or maybe just as a measure against intersample clipping. some DAPs make headroom by default, some lower the gain only when we turn ON the EQ or whatever, and a few I guess still let us clip the signal if we set a few things poorly.
    this could deserve to go at the top of the list of things that could readily result in audible change. above my list of stuff less likely to be heard.
  9. bigshot
    The level changes don't come within the digital domain, they come in at the output stage when it's an analog signal. The output level of consumer products isn't calbrated terribly accurately. Also, on that end you have volume pots that alter it further. Any line out or headphone out has to be level matched. The easiest way to do it in this case is take the analog line out from the two DACs and balance them, then run them through a switcher to a single amp or headphones for monitoring. You wouldn't need to level match the amp for the headphones because that would be the same for the two DACs.
    Last edited: Apr 10, 2019
  10. castleofargh Contributor
    OP is discussing a case of using 2 DAPs as source connected through USB into the same DAC.
  11. bigshot
    All I saw was the two DAPs part. I was assuming two analogue outputs. If the sound is getting converted in a separate DAC, then all the DAPs are doing is just passing the digital file along. Assuming the two DAPs are playing the exact same file, that can only be one of two things, perceptual error due to too long a gap of time between samples, or one of the DAPs is defective.

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