I have been having an intermittent problem where my microphone just drops out arbitrarily on Linux and I can’t access it anymore. It turns out that this was actually due to a dodgy USB hub inside the motherboard of my computer.
I was finding that looking at /sys/bus/usb/devices/1-5.1/power/runtime_status (this will be different on your machine) was showing “error”. Oh dear, said Paddington. The symptom was that the device wasn’t visible as an audio microphone input. I couldn’t use the microphone, and lots of USB devices were all over the place. For a short while the microphone would appear in the volume control list, but I could not get any signal through it.
The solution in the end was actually quite simple, I just needed to reset the USB “hub”. For me, this is what worked:
sudo bash -c 'usbreset 001/003; sleep 2; usbreset 001/002'
systemctl --user restart wireplumber pipewire pipewire-pulse
Not a very exciting post I know, but someone might be helped by it.