I've seen many USB DACs stating they incorporate "galvanic isolation" & although correct to some extent, it's a case of the "closing the barn door after the horse has bolted"
The reason being that this "galvanic isolation" is performed after the USB receiver which has some effect but is not the optimal solution
Optimal USB isolation is needed before the USB receiver, on the USB signal lines particularly (D+ & D- lines). It would appear that USB is a pseudo differential electrical protocol & needs particularly low noise, well formed signals in order that the downstream I2S signal output from the USB receiver stage is low in jitter. Isolating a jittery I2S signal does absolutely nothing to eliminate the sonic effects of this jitter, in fact isolation usually adds its own jitter.
Even some of the best DACs can be improved sonically with USB signal cleansing - see this report on the Mola Mola https://www.stereo.net.au/forums/topic/117214-mola-mola-dac/?page=2
"To me using the Uptone Audio regen eliminated what was otherwise an overly cool, sterile sound from the MolaMola DAC."
"the Mola Mola DAC with the regen in the chain sounds more fluid and musical to me."
Now this is without USB isolation as he couldn't get the Mola Mola to work with USB isolation only with USB signal cleansing via the Regen
The reason being that this "galvanic isolation" is performed after the USB receiver which has some effect but is not the optimal solution
Optimal USB isolation is needed before the USB receiver, on the USB signal lines particularly (D+ & D- lines). It would appear that USB is a pseudo differential electrical protocol & needs particularly low noise, well formed signals in order that the downstream I2S signal output from the USB receiver stage is low in jitter. Isolating a jittery I2S signal does absolutely nothing to eliminate the sonic effects of this jitter, in fact isolation usually adds its own jitter.
Even some of the best DACs can be improved sonically with USB signal cleansing - see this report on the Mola Mola https://www.stereo.net.au/forums/topic/117214-mola-mola-dac/?page=2
"To me using the Uptone Audio regen eliminated what was otherwise an overly cool, sterile sound from the MolaMola DAC."
"the Mola Mola DAC with the regen in the chain sounds more fluid and musical to me."
Now this is without USB isolation as he couldn't get the Mola Mola to work with USB isolation only with USB signal cleansing via the Regen