How can I find out which sound subsystem is currently in use?

Question

linux

This is the first time I've come across this need. Help advice.

Answer 1

PulseAudio over ALSA if the default state is without obvious tweaks.

Answer 2

The kernel may have ALSA (most likely) or OSS (rare). On top of what's in the core, PulseAudio usually runs. Applications can use PulseAudio or ALSA directly.
If pactl info shows anything, then PulseAUdio is running.