Guide on using an USB audio device with Qubes 4.1

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I am not good at writing guides, but will do my best.

The point of this guide-for-noobs-like-me is, by using the tips from a link in the OP to set up a separate sys-audio-like domain for USB audio cards in Qubes OS 4.1, so to avoid the need to attach-detach USB card from qube to qube when needed.
Instead, a single qube will be set, to which the USB card and microphone will be permanently attached, so all other qubes could use USB card without the need of direct attach.
I have named the domain usb-audio for obvious reasons and analogy.
Thanks to original contributor stroberrysugar.

I haven’t thoroughly searched the forum for such a guide, so please apologize if the one already exists.

Introductory remarks

I) Whole procedure is described as if sys-audio is already set up, like it was on my system. No step described is depended on this, so applicable even when there’s no sys-audio set.

II) I have tried to create working usb-audio domain based on fedora-35-xfce, but didn’t succeed at first (which is related to my remarks in OP). Then, I successfully created it based on fedora-34-xfce, on which my sys-audio is already based. The fact made me to compare lists of all installed packages in both versions of Fedora, to diff them and to install in fedora-35-xfce those packages found only in fedora-34-xfce which were installable for v35. After this, I was able to successfully build working usb-audio qube based on fedora-35-xfce. Basically, you should take care that in both you have installed following

packages
  • alsa-plugins-pulseaudio
  • alsa-utils
  • pulseaudio(-utils)
  • pipewire(-uitls)
  • qubes-audio-deamon
  • webrtc-audio-processing
  • xfce4-pulseaudio-plugin
  • pavucontrol

List is not exhausted, nor all the entries are mandatory most probably. It’s just what I have of them installed and found significant to mention.

How To

  1. Create usb-audio app qube based on fedora-34-xfce, or fedora-35-xfce.
  2. I have used default settings, except I have set memory balancing from 400-800MB purely guessing, still to investigate. The less the better.

For those who don’t have sys-audio, steps 3. and 4. are most probably unnecessary, but will not harm if taken just in case.

  1. Set dom0 as default audiovm for usb-audio:

[user@dom0 ~]$ qvm-prefs usb-audio audiovm dom0.

  1. Set dom0 as the default audiovm for any other qube, at least for one more which will serve to test. Let’s call it audio-test.

  2. In dom0, add a new null sink (my_usb_audio):
    [user@dom0 ~]$ pactl load-module module-null-sink sink_name=my_usb_audio

  3. Start playing some audio in audio-test qube.

  4. Start usb-audio qube, via Qube Manager, or via qvm-start usb-audio in dom0 terminal.

For those using sys-audio, steps 8. and 9. are most probably unnecessary to take, since there should be no sinks in dom0, and the newly created sinks would be the default ones.

  1. In dom0, open pavucontrol and in the Playback tab change the output device of the audio-test to the null sink you just created.
  2. In dom0 go to the Recording tab and change the input device of usb-audio to the monitor of the null sink you just created.
  3. Attach both the USB audio device and dom0:mic to usb-audio via device widget, or in terminal:

[user@dom0 ~]$ qvm-usb attach --persistent usb-audio sys-usb:<BDF_of_the_USB_audio_device>

[user@dom0 ~]$ qvm-device mic attach --persistent usb-audio dom0:mic

We need to attach dom0:mic in order usb-audio could actually receive the audio from the null sink monitor in step 9.
Please note that --persistent is purely optional, and it should serve both USB audio device and microphone to be automatically attached on usb-audio start.

  1. In usb-audio, we need to find the name of the USB audio device. This should serve the best:
    [user@usb-audio ~]$ pacmd list-sinks | grep -e 'name:' -e 'index:'

The output should be something like:

index: 0
name: <vchan_output>
* index: 1
name: <alsa_output.usb-0e2d_USB_Sound_Device-00.analog-stereo>

So, there’s the name of our USB device to be used in final step.
The * in front of the index indicates the current default output.

  1. In usb-audio, we now need to create a loopback module in PulseAudio to redirect audio from the mic to the USB audio device:

[user@usb-audio ~]$ pactl load-module module-loopback source=vchan_input sink=alsa_output.usb-0e2d_USB_Sound_Device-00.analog-stereo

  1. You should now hear the sound of your beloved song played in test-audio qube.

Final note

Any qube for which dom0 is set as default audiovm will use now usb-audio without any additional actions taken. It’s even possible to create a separate sink per qube, so to avoid mixing sounds from 2 or more qubes at the same time. It is just needed to select proper output and monitor sinks in dom0's pavucontrol.

To do

Sinks won’t survive Qubes reboot, so they have to be recreated upon each start up. This can be automated via scripts on start up, but I am not willing at the moment to invest more time for this, since I’m preparing my laptop for a full transition to a sys-gui-gpu.

You are welcome and feel free to contribute the scripts to automate the process on startup. Salt-like formulas preferred so we could have them more and more in the forum thus be able to faster learn it.

Please let me know if anything have to be corrected in this noobs-guide, either it’s terminology, or essentially.

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