mutesysvolume [action] {Component} {Device Index}
Mute/unmute the system volume.
In the [action] parameter, specify 1 for mute, 0 for unmute, or 2 for switching between mute and normal state.
The second parameter is optional, and you can specify one of the following sound components: master, waveout, synth, cd, microphone, phone, aux, line, headphones, wavein. The default value is 'master' (for master volume). (...)
{Device Index} is an optional parameter that specifies the sound device index. This parameter is useful if you have more than one sound card. If you don't specify this parameter, the default sound card in Control Panel is used.
Examples:
mutesysvolume 1
mutesysvolume 0
mutesysvolume 2 waveout
mutesysvolume 1 master 1