Command to mute and unmute a microphone
Go to
System Preferences then Keyboard and click Shortcuts then Custom Shortcuts:
Click on Add
Fill in:
Toggle microphone
and
amixer set Capture toggle
For usb webcams you need to chose device (-c 1), or maybe another number.
amixer -c 1 sset Mic toggle
Click Apply and then associate a new key with this command (e.g. the Pause/Break key).
You can mute the microphone with
amixer set Capture nocap
and unmute the microphone with
amixer set Capture cap
amixer set Capture toggle && amixer get Capture | grep '\[off\]' && notify-send "MIC switched OFF" || notify-send "MIC switched ON"