You don't need to rely on the DAC to tell you what is happening. You can check exactly the situation in pulseaudio using the following command in the terminal while audio is playing:I don't really understand Linux, but I think you've set the resampling rate in the PulseAudio output settings and it's being output to USB at that value.
ALSA seems to have a mechanism to resample everything to the same frequency (48000 by default) when software mixing is enabled.
MOTU M4 supports 44.1 ~ 196kHz input, but since there is no display, the actual operation is unknown. Maybe it's working at a resampled frequency.
In the case of PCM / DSD playback, Windoes installs the XMOS ASIO driver provided by Topping to perform native playback. If you use only PCM, you can play it in WASAPI mode without a driver.
Code:
pacmd list-sink-inputs
This shows (among many other things):
- the source sample rate and bit depth
- whether resampling is in use
- the module used for the resampling
Code:
cat /proc/asound/card0/pcm0p/sub0/hw_params
Running the commands show that the Motu M4 output sample rate is the same as the source sample rate, while the D10 output sample rate is always the pulseaudio default sample rate; the source audio is resampled to the pulseaudio default sample rate before it is sent to the D10. Both devices use the same set pulseaudio configuration.
If you review the gitlab link in my first post, the speculation is that the ALSA query used to retrieve the DAC's supported sample rates doesn't work properly in certain circumstances, leaving the default sample rate as the only option. It doesn't happen for all DACs using pulseaudio or ALSA. I can't say whether it happens for DACs other than the D10 because I haven't looked for them. It does seem to happen to others using the D10 with pulseaudio as I've found 4 different examples as you can see from my first post.
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