Difference between revisions of "ALSA"
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*/proc/asound/version version and date the ALSA subsystem | */proc/asound/version version and date the ALSA subsystem | ||
+ | As an example, this break down the output of | ||
+ | lsof /dev/snd/pcm* | ||
+ | we see (this is an example, yours will be different) | ||
+ | fungame 4854 nicolep mem CHR 116,10 632 /dev/snd/pcmC0D0c | ||
+ | fungame 4854 nicolep 68u CHR 116,10 0t0 632 /dev/snd/pcmC0D0c | ||
+ | |||
+ | which is | ||
+ | * fungame - the process name, in this case a game that is using ALSA to do sound (play or capture) | ||
+ | * 4854 - PID | ||
+ | * nicolep - the username owns the process | ||
+ | * /dev/snd/pcmC0D0c - device files are what applications connect to in order to perform sound operations | ||
+ | |||
+ | The device file here is 'pcmC0D0c' | ||
+ | * pcm is the service name or type, ours is clearly a pcm which is an alsa stream type | ||
+ | * C0 is the card number, C for card and 0 as the first card (numbering starting with 0 and going up 1,2,3...) | ||
+ | * D0 is the device number, D for device and 0 as the first device | ||
+ | * c indicates it is a capture device. If it is a 'p' then it is a PCM playback device, if it is a 'c' then it is a PCM capture device. | ||
Revision as of 18:35, 25 March 2021
ALSA or the Advanced Linux Sound Architecture provides audio support for Linux. It is a replacement for the old OSS linux sound system. The Alsa-utils package contains both the Alsamixer and Amixer utilities. Various linux distributions once used the Open Sound System, or OSS until ALSA superseded it. ALSA provides kernel driven sound card drivers and bundles a user space driven library for application developers.
You can control the audio properties of your sound cards through:
- Alsamixer-The graphical interface for ALSA
- Amixer-The command based utility for ALSA
Contents
ALSA CLI Utilities
alsamixer
ncurses based utility with visual representation of various levels.
alsamixer
Enable the microphone: switch to the Capture tab with F4 and enable a channel with Space.
mixer
Command line, operation performed per command.
amixer -c [card-number] set [control] [value]
To see what controls you can manage
amixer scontrols
If you are sudo there are more controls available
sudo amixer scontrols
apulse
The apulse utility lets you use ALSA for applications that support only PulseAudio for sound.
aplay
Alsa play - play an audio file
arecord
We can test the default audio input device, or the only audio input device on a simplistic configuration
arecord -vvv -f dat /dev/null
Watch while the audio input levels are displayed as a percentage.
We can specify an audio input device
arecord -vvv --device="hw:1,0" -f dat /dev/null
You can display a list of CAPTURE Hardware Devices. To figure out what audio input device is at hw: card,device use the following command
arecord -l
The output look for "Card X" and on the same line "device X" to know the card,device combination to specify.
speaker-test
as the name implies
Example: Testing audio input / microphone input Excerpt from Troubleshooting Linux Sound by Steve Litt troubleshooting guide"
Steve says, "The speaker-test program provides a nice, easy way to provide input for your sound system. When used with no arguments, it simply supplies white noise to both speakers."
Testing an M-Audio external USB sound board it was unclear as to whether or not stereo separation was functional or if the audio was monaural (mono) since the balance slider on audio players seemed to have zero impact. Elimination of audio application software is advised to find if ALSA and your wiring are correct. Use this command:
speaker-test -c2 -t wav
As Steve advised in his article the command will alternate between left and right speaker audio dialog in a loop allowing you to listen and determine if the sound is coming from the speakers, the correct speakers and that you have functional stereo separation. You may find it useful to ensure you do not have intended left speaker audio coming out of your right speaker. If you have more than 2 channels, put the number of channels in the -c argument.
Be advised the article is very informative and we hope it remains online as well as The Steve Litt Diagnostic Tools he provides there. Thanks Steve!
Configuration
All files in /proc/asound are created and used by ALSA. these files describe the sound card or related devices.
- /proc/asound/cardX/ (where X is the sound card number, from 0-7) : a cardX directory exists for each sound card
- /proc/asound/cards is the list of registered cards
- /proc/asound/dev/ is a directory listing the specific device files used by programs for sound operations if your system uses devfs
- /proc/asound/devices is a read-only file showing the registered alsa devices such as digital audio capture and playback
- /proc/asound/hwdep hardware dependent controls
- /proc/asound/meminfo shows kernel level memory space
- /proc/asound/modules lists registered ALSA soundcard drivers for specific things such as each soundcard
- /proc/asound/oss/ old oss emulation
- /proc/asound/pcm helpful for identification of hw:0,0 labels, technically they are streams/devices but think of it as how you find the hw:X,X values you are looking for.
- /proc/asound/seq/ sequencer data
- /proc/asound/timers a list of timers ALSA knows about, and also describe which ones are in active use. (could this be useful in resolving Device or resource busy issues?)
- /proc/asound/version version and date the ALSA subsystem
As an example, this break down the output of
lsof /dev/snd/pcm*
we see (this is an example, yours will be different)
fungame 4854 nicolep mem CHR 116,10 632 /dev/snd/pcmC0D0c fungame 4854 nicolep 68u CHR 116,10 0t0 632 /dev/snd/pcmC0D0c
which is
- fungame - the process name, in this case a game that is using ALSA to do sound (play or capture)
- 4854 - PID
- nicolep - the username owns the process
- /dev/snd/pcmC0D0c - device files are what applications connect to in order to perform sound operations
The device file here is 'pcmC0D0c'
- pcm is the service name or type, ours is clearly a pcm which is an alsa stream type
- C0 is the card number, C for card and 0 as the first card (numbering starting with 0 and going up 1,2,3...)
- D0 is the device number, D for device and 0 as the first device
- c indicates it is a capture device. If it is a 'p' then it is a PCM playback device, if it is a 'c' then it is a PCM capture device.