Here is a small set of files that tests the quality of the audio recorded from two DACs. It includes level matched and synchronized samples for ABX testing (I do not think there will be many positive results, though, maybe some for the onboard), but perhaps more interesting are the "difference" files, which were created by matching the levels, frequency and phase response, speed, and delay of the files as accurately as possible, and then subtracting the original from the recorded sound. This makes the artifacts of the DAC much easier to hear. However, the synchronization is not perfect (it cannot really be, since the DAC and ADC clock frequency slowly changes over time by a small amount), so it is still possible to hear the original audio, but it is significantly attenuated.
For more information, see also this and this post. For the Xonar D1 difference signal, I used somewhat better synchronization, but it is limited by the very low frequency DAC/ADC jitter (note how the sound fades in and then out over time as the delay between the samples changes).
D1_A.flac - the original file resampled to 96 kHz
D1_B.flac - the recorded audio (level matched, pitch corrected by a factor of 1.00000592658676, and synchronized with the original)
D1_diff.flac - difference signal amplified by 60 dB
Realtek ALC887 onboard audio
loopback.7z - includes A.flac and B.flac, and various source files
diff40dB.flac - difference signal amplified by 40 dB
Edited by stv014 - 1/30/13 at 12:14pm