Plugins
ALSA consists plugins.
The hw plugin does not processing, it accesses the hardware driver.
The plug plugin performs channel duplication, sample value conversion and resampling (when necessary because not supported by the hardware).
The file plugin writes sample data to a file.
Cards, devices, subdevices, interfaces
Cards
A card is either a physical or logical kernel device that is albe to record, process or emit sound.
ALSA counts up to eight cards, numbered from 0 to 7 or alternatively identified by an ID.
Devices
Each card has devices whose numbers again start with 0.
These devices have a specific kind such as
- playback
- capture
- control
- timer
- sequencer
The device »level« is where most of the hardware access takes place.
Subdevices
A device might have subdevices.
A subdevice, if available, specifies a sound end point.
Interfaces
An interface specifies an asla protocl to a card/device/subdevice triple.
An interface string thus might look like interface:CARD=0,DEV=1,SUBDEV=1.
Utilities
speaker-test is a test tone generator for ALSA.
alsactl allows to save settings for a device.
amixer to make adjustments to devices volume and sound controls.
alsamixer is the
ncurses version of
amixer.
acconnect and aseqview to make midi connections and view the list of connected ports.
aplay plays back a sound file.
arecord records a sound file.
alsaconf