SUMMARY

This is a feature request. 

Currently, there's no GUI to control if an audio device should output as mono. On my computers (Pipewire), there are many profiles to select between stereo or surround in the audio applet, but none to downmix audio to mono.

Usecases:

- If one audio output is malfunctioning and only one side is working (defective earbuds, headphones, etc.), downmixing the audio to mono can be useful to make sure the user can hear both channels from only one speaker. Both Windows and macOS have the option to downmix audio to mono in their Accessibility Settings for this reason.

- While producing audio, it might be necessary to test how a sound will sound when played with different channels. I've run into this issue while designing the new Plasma sound theme: I had to use Windows in order to test how the sounds would sound in Mono because Plasma didn't have the option to change that.

Technically, it's possible to downmix to mono using Easy Effects or Qpwgraph (at least on Pipewire), and it's also possible to do that with Pulseaudio using the command line and changing configuration files, but it's not a good user experience to have to download third-party software or use the command line to control something other systems like Windows, Android, macOS, and iOS offer natively. 

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As far as I can tell there are some ways to set the audio to mono with Pulseaudio. I couldn't find anything about doing that natively on Pipewire, only through third-party programs like Easy Effects or qpwgraph.

Here's some information I found online about downmixing to mono on Pulseaudio:

https://askubuntu.com/questions/17791/can-i-downmix-stereo-audio-to-mono/99960#99960
https://forum.manjaro.org/t/how-to-turn-audio-to-single-channel/53838

Thank you for reading.