UPDATE: problem is still preset … still trying to find what is going on.
After a recent update on my debian workstation, I had spurious sound volume changes, only with line out, no matter my usb headset either plug in or out (but when I listen with the usb headset, there was no problem).
I did a few days of search, first is where to dig for a problem, then how to check pulse audio log, then how to check alsa, and acpi.
And the problem was … HARDWARE !
So the problem comes from spurious front jack headphone event as shown with the following logs. These plug/unplug event mess alsa and jack with volumes … maybe it can be fixed with some configuration to restore correct sound after unplug, but the problem is that I do not have front jack used at all.
(I use the explanation here to have pulseaudio log, tldr:
systemctl --user stop pulseaudio.socket #since the socket relaunch pulseaudio all the time. echo autospawn = no >> ~/.config/pulse/client.conf LANG=C pulseaudio -vvvv --log-time=1 > ~/pulseverbose.log 2>&1
$ cat pulseverbose.log | grep Jack | grep plug (6391.015| 6.180) D: [pulseaudio] module-alsa-card.c: Jack 'Front Headphone Jack' is now plugged in (6391.036| 0.018) D: [pulseaudio] module-alsa-card.c: Jack 'Front Headphone Jack' is now unplugged (6476.288| 67.655) D: [pulseaudio] module-alsa-card.c: Jack 'Front Headphone Jack' is now plugged in
$ sudo acpi_listen jack/headphone HEADPHONE plug jack/headphone HEADPHONE unplug jack/headphone HEADPHONE plug jack/headphone HEADPHONE unplug
I tryied to plug/unplug an headset in the front jack, and the event do not coicinde … so I unplug the front jack from the motherboard, TADAA ! no more spurious event.
Next step is to check cable conductivity, and clean with contact cleaner, but nevermind, I do not use this jack anymore.
Take home message, sometimes events are related sometimes not … when dealing with computer events used to be linked (the update mess up a lot of things, because of gnome-shell update and incompatibility with some plugins), but this one was not, and it slow down a lot the resolution (since most of my net searches have gnome 3.38 in the key words, or debian update …) After a few days, I think of the problem differently, as how I can track what is going on rather than something is not correctly installed.