alsamixer is part of alsa-utils and is run by entering
alsamixer &
on the command line.
Troubleshoot
- Channels are muted
On some buggy installation, alsa mutes all channels and sets the volume to 0 for all of them. Start the command line alsamixer program and unmute (press m) and change the volume of the channels you are interested in (use the arrow keys to navigate and change volume). You can unmute preferably the Master and PCM channels.