Digital Audio Output Differences? Is USB Audio Really The Top-notch?

USB is a new comer… when PCs joined in the audio arena. Typically DACs had no USB input. At first DACs did not support them… it is packeted info… not just a digital bit stream.

So, audio equipment popped up that only supported USB, then the USB input was added to higher quality equipment. Which is better is completely dependent on your DAC / source combination. Sometimes it seems that which ever is the higher quality DAC or source), but that doesn’t always work. I have a top quality streamer and DAC and it is really hard to tell the difference. I give the nod to AES.

Trying to understand why I hear a difference between USB vs  spdif and AES inputs.   I compared a vintage tube dac with a current solid state dac.   I have a Levinson 31.5 reference transport.   I connect it to a Sonic Frontiers MkII DAC via optical SPDIF or a Schitt Modius dac via AES.... I can't say there is much of a difference between the two dacs and the differences are subtle.   Relevant to this thread...   I never developed a preference between comparing the optical and coax connections on the SF and had no preference comparing the Coax and AES inputs on the Schitt Dac.   

What surprised me was the difference between streaming a flac file of a cd to the USB input of the Schitt versus the cd played on the transport via AES to the DAC.  I can't say one is better then the other... they are just different.      The transport to the Schitt (or SFdac)  is a bit more velvety sound quality while the USB is a bit more crystalline.   Why such a difference?....

I can imagine a parade of reasons...and none make a lot of sense to me since I can't say the USB sound is good or bad....   just different...and I have no basis to understand the differences.     So.... explanations  like  Jitter from the transport to Dac.   Noise from the PC polluting the USB DAC or jitter in the USB interface etc etc  are all theoretical to me and make no sense.   Thoughts would be appreciated!

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USB is fundamentally a different communication method from SP/DIF and AES. USB needs packet conversion, retiming to a bit stream… so that is a function that now falls on the DAC. SP/DIF are the same through different connection types. Optical is usually not as good as it has to go through a electrical to optical conversion, and then back.

...mmm....What always and still pesters me is the apparent disinterest in optical ICs'...

It would seem anything that can carry a SOTA video stream would be SOP for audio....

....or did that ship 'sail', left in reverse, and take out the dock? ;)

Curious, if anyone feels like comment....

All eyes (ears occupied), J