alsamixer is a graphical mixer program for the Advanced Linux Sound Architecture (ALSA). It is used to configure sound settings and to adjust the volume. It has an ncurses user interface and does not require the X Window System. It supports multiple sound cards with multiple devices.
The top-left corner of alsamixer is the area to show some basic information: the card name, the mixer chip name, the current view mode and the currently selected mixer item. When the mixer item is switched off, [Off] is displayed in its name.
Volume bars are located below the basic information area. You can scroll left/right when all controls can’t be put in a single screen. The name of each control is shown in the bottom below the volume bars. The currently selected item is drawn in red and/or emphasized.
Each mixer control with volume capability shows a box and the current volume filled in that box. The volume percentages are displayed below the volume bar for left and right channels. For a mono control, only one value is shown there.
When a mixer control is turned off, M (mute) appears below the volume bar. When it’s turned on, O in green appears instead. You can toggle the switch via m key.
When a mixer control has capture capability, the capture flag appears below the volume bar, too. When the capture is turned off, ——- is shown. CAPTURE in red appears when the capture switch is turned on. In addition, L and R letters appear in left and right side to indicate that left and the right channels are turned on.
Some controls have the enumeration list, and don’t show boxes but only texts which indicate the currently active item. You can change the item via up/down keys.