Excellent comments by all, IMO, on an issue that by its nature is highly speculative.
Even if an asynchronous USB DAC is being used, conceivably high frequency noise transients riding on the USB signal pair and/or the associated power and ground lines could couple past the DAC's input circuits to internal circuit points, where they could affect timing of the DAC chip itself, and/or subsequent analog circuit points. Galvanic isolation would help in that regard, as you noted, but it is not always employed, and who knows how effective it is in any given situation?
And then there is the possibility, perhaps somewhat more remote but conceivably still possible, of differences in rfi resulting from those format-sensitive noise transients, the rfi perhaps bypassing all of the digital circuits that are involved and coupling onto sensitive analog points elsewhere in the system.
Best regards,
-- Al
11-23-11: DtcWhat about my hypothesis, that differences in the processing that is performed when playing the different formats result in differences in when and how often "Speed Step" and related power conservation features are called into play (unless the user goes through the steps that are necessary to disable those features), in turn resulting in significant differences in computer-generated noise transients, in turn resulting in differences in jitter and/or noise coupling?
I agree that networked solutions can provide better isolation that direct connections. Remember, I am not talking about audio streams in general, but the difference between FLAC and WAV files. I am not willing to say that computers routinely make computational errors when compressing and decompressing FLAC files and therefore WAV files are better. If people think they hear a difference, that is up to them. But I have yet to hear a detailed explanation of why that happens that makes sense.
Even if an asynchronous USB DAC is being used, conceivably high frequency noise transients riding on the USB signal pair and/or the associated power and ground lines could couple past the DAC's input circuits to internal circuit points, where they could affect timing of the DAC chip itself, and/or subsequent analog circuit points. Galvanic isolation would help in that regard, as you noted, but it is not always employed, and who knows how effective it is in any given situation?
And then there is the possibility, perhaps somewhat more remote but conceivably still possible, of differences in rfi resulting from those format-sensitive noise transients, the rfi perhaps bypassing all of the digital circuits that are involved and coupling onto sensitive analog points elsewhere in the system.
11-22-11: Mapman
But the format itself does not correlate to sound quality in general though. Lots of other crap can go wrong and chances are it does so differently because of different hardware and software processing scenarios for different formats. The devil is all in the details. But not in the source format itself. If processed properly, the results are the same. That can be a big if though.
11-23-11: MapmanWell said! Agreed 100%.
Most general purpose computers have no business being connected directly to your high end audio gear! Think of this [network playback] as a form of isolation, similar to other steps you might take to isolate your rig from potential sources of noise.
Best regards,
-- Al