Originally Posted by cel4145
I would disagree because it would seem like the noise floor could vary depending on the implementation (the computer). It might be subtle or might be more noticeable. When I got the ODAC, I thought it sounded a little bit darker in depth of silence than the STX (otherwise, pretty much the same in SQ). But I how would I have known that if I didn't have anything to compare the STX to?
It should be possible to tell silence apart from non-silence in a listening test. You can compare the STX to not having the headphones plugged into anything, or switching the card to line output (which disconnects the headphone jack with relays). If you mean the difference is so small that you cannot tell if there is any noise, even while there is no music to mask it, then why worry about it ? On the other hand, if you mean the ODAC has better "depth of silence" (without any actual identifiable noise on the sound card) specifically while playing music, then sighted listening could have been a problem.
Of course, it is also possible to create a loopback recording from the headphone output (this does not give reliable results with an external amplifier that might be susceptible to ground loop issues), and then play it back at an amplified level just to be sure if there is no interference.
Note that the STX could have audible noise, regardless of the computer, with some very sensitive headphones and IEMs, especially at 44.1 kHz sample rate. This is not interference, but the "normal" noise floor of the card, which is relatively high on the headphone output because it does not have any analog volume or gain control. It is recommended to use the built-in headphone amplifier with medium to high impedance headphones anyway, because of the output impedance.