On Saturday, December 26, 2020 3:48:15 A.M. EST Jan Girke wrote: > Remove the hdd/ssd from the laptop and use a spare to downgrade until > you find the version it worked and then compare the two states.
I did more-or-less this, but instead using Debian live-CD images on a USB stick, and after some tedium I eventually realized that even the weekly live- CD of Testing (built yesterday) worked just fine. After some more searching I figured out what the difference was: the "Loopback Mixing" setting in alsamixer. It's apparently disabled by default, but for some reason mine had migrated to enabled. Enabling it seems to dictate that headphone levels are controlled through the "Speaker+LO" channel instead of the "Headphone" channel. Setting it back to disabled, and things are now back to normal. Mystery solved! Best, Brendon
