Meh, I already have a global mute shortcut. I have a keyboard shortcut for this script I found somewhere that toggles mic audio capture in ALSA.

#!/bin/bash

mic_on=$(amixer get Capture | grep '\[on\]')

if [ "$mic_on" = "" ] ; then

amixer set Capture toggle && paplay /usr/share/sounds/ocean/stereo/device-added.oga

else

amixer set Capture toggle && paplay /usr/share/sounds/ocean/stereo/device-removed.oga

fi