Acer Chromebook 15 CB3-532 Debian Testing microphone not working

[Alexander van der Leun <alex@vdleun.net>]

Hi all,

This week I converted an Acer Chromebook 15 CB3-532 from ChromeOS to Debian
Testing. Mostly everything worked correctly out of the box. After some
fiddling I got video acceleration working and Gnome now works 95% okay;
still some problems with playing video in Google Chrome, but that's okay
for now.

What's not working at the moment is the microphone. Or, better worded, it
only records noise when using arecord.

This is the hardware:

card 1: chtrt5650 [chtrt5650], device 0: 3 []
  Subdevices: 0/1
  Subdevice #0: subdevice #0
card 1: chtrt5650 [chtrt5650], device 1: Deep-Buffer Audio (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0

Using alsamixer, I put the recording volume way up, but still only noise.

I've followed a couple of forum posts on the internet with people having
the same problem (with the same hardware), but nothing works. I've taken a few
configuration files from GalliumOS for my notebook, but that also didn't make
the microphone work.

That's why I want to start with a fresh approach, but don't know where 
to start. I've been away from Linux on the desktop for quite some years 
and things have changed, such as Alsa UCM and PipeWire. AFAIK, 
PulseAudio is still in someway involved with the audio on Debian 
Testing, as pavucontrol works.

Can someone point my out to where I should start searching for a solution?
Let me know if more information is required.
 
Thank you.

Best regards,
Alexander