I've played around with jack in the past, but I have never really been successful with it because it feels overwhelming and it doesn't allow my computer audio output to continue functioning while jack is running. Trying to play songs in my media player has them hang at 0 seconds attempting to play them; presumably they are writing PCM or something to pulseaudio or alsa and that write is never completing.
Is there a way to have jack running most or all of the time in the background while still being able to hear computer audio output?
In my case, I have a USB audio interface (a Focusrite Scarlett) which is connected to a pair of speakers which I use as my default audio output, but I'm not sure whether the output type (i.e. USB or an internal sound card) matters here.
I'm on Ubuntu 20.04 LTS running the latest HWE kernel (actually elementary OS Odin, but based on Ubuntu 20.04).
EDIT: I was able to completely bypass all of this by using PipeWire.
PipeWire is a low-latency audio system which can speak PulseAudio, ALSA, and Jack protocols, and can easily replace both PulseAudio and Jack. I replaced my desktop's PulseAudio server with PipeWire, it isn't too hard, and enabled PipeWire for Jack as well, so now everything goes to one unified place and I don't need to do silly workarounds to make things work, they just do, and everything is none the wiser.
I've written up how to do this for my distribution, elementary OS 6, in this Gist.