I wanted to carry out more in-depth tests of the Win audio system.
I have Win 11 latest version, with Virtual Cable HiFi ASIO Bridge installed to make loopback measurements with REW.
Since I'm tormented by the fact that the Win mixer doesn't automatically switch the frequency, I wanted to include the resampling in the test, i.e. from 44.1/16 to 192/24, representative of normal playback with Spotify for example. So I set Virtual Cable to 192kHz both in and out.
In REW I set 44.1kHz with default JAVA driver (so no Exclusive Mode) and then played three types of signals (16 bit dithered) to make sure I don't see just THD+N but also TD+N, which I feel hasn't been checked in this thread.
For TD+N I used multitone and triple tone (10.5 + 19 + 20 kHz). However, the signal parameters are indicated in the following screens.
TO NOTE for multitones are the peak dBFS of signal, i.e. those indicated in small print at the bottom right of the RMS signal level box.
Also note the peak dBFS of captured signal in top right box, as well as the distortion in the upper left box on the graphs.
The interesting thing is that with triple tone -0.1 dBFS pk is enough to avoid any distortion, while with single tone -0.2 dBFS pk is needed.
With multitone instead you need -2.77 dBFS pk. Above that value the TD distortion reaches 0.75%. Unacceptable.
I'm not an expert on signals but it seems to me that with complex signals at least -3 dBFS peak is needed to avoid the Windows limiter. The single tone test is not sufficient to show the intervention threshold.
What is not clear to me is on the basis of which level the limiter intervenes.
However, the positive thing is that without the limiter the resampling from 44.1/16 to 192/24, that always occurs in these test, does not involve any audible distortion.
To evaluate the goodness of the resampler it would be necessary to do other tests, I know. But for people like me who are concerned about the fact that normal streaming music players don't support really bit perfect drivers (see WASAPI Excl. mode of Amazon Music) know we can upsample everything to 192khz without audible distortion is a nice relief.
For the record, I also made measurements with 192kHz signals in order to avoid resampling, and it changes about 0.005% THD in favor (worst case with multitone signal).
If I have done something wrong, or there are any distortions not detected/detectable by REW RTA please let me know, thanks.
Here the results: