If you have a system with more than stereo (say 5.1) then by default pulseaudio upmixes all sources with fewer channels by simply duplicating all the channels o

If you have a system with more than stereo (say 5.1) then by default pulseaudio upmixes all sources with fewer channels by simply duplicating all the channels on the same side and mixing everything to the centre channel. This makes it impossible to listen to music recorded with any meaningful stereo separation. The workaround is to mute all the extra channels. There is an option to disable upmixing entirely but that triggers at least a couple of bugs. One involves the VU meter indications (shrug). The other causes pulseaudio to emit silence instead of mono streams (fatal). This bug has been open for over a decade now. At least one patch has been submitted and shrugged off. If you look at the tracker you will see lots of bugs like these where knowledge of the entire system is required to fix them. What seems to have happened is that once the original developers left, some bugs became eternal.