mutes the microphone so that only the Director can unmute it; the guest cannot unmute.
full volume - default
value will be applied as a percentage.
Can be used to have a guest muted by default when joining a room.
Can be remotely controlled by the Director if in a room; the guest cannot unmute themselves
Only applies to the first audio-source selected by a guest, if there is more than one selected.
If audio processing is on, then this should be available by default for the director to remotely control.
The gain function will NOT work if web-audio node processing cannot be enabled