My son bought a $400 DAC that claimed to have async USB support but immediately found out that he got PC noise through it just like his other solutions. So I instrumented it and this is what I found.
Feeding it a single tone over S/PDIF:
I wouldn't expect this kind of jitter in a $25 DAC let alone one for $400.
So we decided to test it with the PC driving it over USB. We played the tone using Windows Media Player:
Didn't think there would ever be a DAC that had more problem with S/PDIF than USB but here we are and the huge jitter spikes are gone. But they are replaced with low frequency ones around our main tone.
To test my son's experience of him hearing system activity, we played the identical track using another player, the Media Player Classic:
All the jitter is gone!!!
We went back to WMP player and let it read the file for a bit and it too settled down to the same performance as Media Player Classic. Clearly system activity disturbed this DAC.
Its brochure brags about "isolation" but the word "galvanic" is not there. This means that it is not isolated from the PC ground and that is feeding into the oscillator causing those correlated jitter spikes.
He sent the DAC back to get his money. When the check arrives, I will mention which DAC it is .
Feeding it a single tone over S/PDIF:
I wouldn't expect this kind of jitter in a $25 DAC let alone one for $400.
So we decided to test it with the PC driving it over USB. We played the tone using Windows Media Player:
Didn't think there would ever be a DAC that had more problem with S/PDIF than USB but here we are and the huge jitter spikes are gone. But they are replaced with low frequency ones around our main tone.
To test my son's experience of him hearing system activity, we played the identical track using another player, the Media Player Classic:
All the jitter is gone!!!
We went back to WMP player and let it read the file for a bit and it too settled down to the same performance as Media Player Classic. Clearly system activity disturbed this DAC.
Its brochure brags about "isolation" but the word "galvanic" is not there. This means that it is not isolated from the PC ground and that is feeding into the oscillator causing those correlated jitter spikes.
He sent the DAC back to get his money. When the check arrives, I will mention which DAC it is .