SOUNDVOL — Display or change the master sound volume.

Syntax:
SOUNDVOL /B /M /O /Q /U volume

/Bbeep after changing settings
/Mmute the sound
/Odisplay the current settings on-screen
/Qquietly
/Uunmute the sound
volumenew volume level, 0 — 100

If /Q is not specified, the current volume will be displayed.

rem  Crank it all the way up:
soundvol 100


See also: the _VOLUME and _MUTE variables, which return the current master sound volume and mute state respectively.