from this post Arvydas write :
For some reason, muting works fine, but unmuting or toggle has no effect. Upon further investigation I noticed that by muting Master channel, “PCM” and “Master Mono” channels are muted too. Unmuting Master does not unmute those two channels.
That work for me on ubuntu 14.04 (qtile WM) to unmute :
pactl set-sink-mute 0 0
to mute:
pactl set-sink-mute 0 1
Updated:
There a lot of reports on this issue Bug #1026331 and Bug #878986 in launchpad, if you mute/toggle master:
amixer set Master mute
Other channels(Headphone and Speaker in my case) will mute also. but if you unmute/toggle Master :
amixer set Master unmute
the Other Channels will stay mute, but if you try unmute Headphone and Speaker channels sound will come back
amixer set Master unmute amixer set Headphone unmute amixer set Speaker unmute