From the ALSA wiki
amixer is a command-line program for controlling the mixer in the ALSA soundcard driver.
amixer supports multiple soundcards. See also the ALSAMixers page and the glossary entry "mixer" for a list of alternative mixer programs.
Usage: amixer <options> command Available options: -h,--help this help -c,--card N select the card -D,--device N select the device, default 'default' -d,--debug debug mode -v,--version print version of this program -q,--quiet be quiet -i,--inactive show also inactive controls Available commands: scontrols show all mixer simple controls scontents show contents of all mixer simple controls (default command) sset sID P set contents for one mixer simple control sget sID get contents for one mixer simple control controls show all controls for given card contents show contents of all controls for given card cset cID P set control contents for one control cget cID get control contents for one control
Jaroslav Kysela let slip an important point about
amixer settings regarding how to enable or disable capture (not playback) settings...
Use: amixer sset Capture cap amixer sset Capture nocap mute/unmute keywords are parsed only for playback