How to listen to microphone output on Linux?

start audio microphone speaker loopback with:

pacmd load-module module-loopback latency_msec=1

add a second:

pacmd load-module module-loopback latency_msec=3000

add a third:

pacmd load-module module-loopback latency_msec=5000

stop the fun afterwards:

pacmd unload-module module-loopback

if the software is missing: apt install pavucontrol (for Debian Linuxes)

You can redirect your audio input to the output using the PulseAudio loopback module:

pactl load-module module-loopback

(https://wiki.debian.org/PulseAudio)