["Sound"]

["ALSA"], the Advanced Linux Sound Architecture, was originally started because the OSS architecture (see ["OSSFree"]) was outdated and the free variant of OSS lacked some drivers available only in the commercial variant. For several years ["ALSA"] was a project separate from Linux. The drivers were added to Linux during the 2.5 development series and became the standard sound driver system in Linux 2.6.

Alsa drivers always start with snd-.

["ALSA"] is not just a set of ["sound"] drivers, it is also a library with an extensible API that gives applications access to the latest features of sound cards (e.g., multiple sound channels, Dolby [AC-3], etc.)

ALSA is backward compatible with ["OSS"].

Find out which sound chipset your soundcard is using

If the card is a PCI soundcard do an '["lspci"] -v' to list all available pci devices. The list will most probably include a reference to a multimedia audio device: that is your SoundCard. You could now have a look at the [http://www.alsa-project.org/alsa-doc/ ALSA soundcard matrix] to find out which driver name can be used for the chipset you found.

If your card was automatically configured to work under Debian with the OSS Free sound drivers, then look at your current /etc/modules.conf file. There will be an entry for the OSS Free module that will also give you a clue of the chipset involved.

Configuration

The latest ALSA packages should work out of the package. The only hitch may be module loading. At one time the ALSA initscript /etc/init.d/alsa loaded modules but this was not well suited to a hotplug environment so that code was removed. Today, hotplug or discover will take care of loading the required ALSA sound modules. Alternatively you can list the modules you need in the /etc/modules file.

Alternatively, you can run the alsaconf utility. This attempts to detect your sound hardware and on the basis of its findings it writes an extra configuration file, /etc/modutils/sound or /etc/modprobe.d/sound, containing lines like these: 

    alias snd-card-0 snd-cs46xx
    options snd-cs46xx index=0

With these module loader configuration entries in place, when the "snd" module loads it will load snd-cs46xx above itself.

Troubleshooting

ALSA loads sound 'cards' in the order it finds them. The first card is always used as the 'default'. If you're unlucky, and a microphone gets selected first, then you're not going to be able to play sounds. You can check the order that ALSA has loaded card with: 

  cat /proc/asound/cards

There are two ways to fix this problem.

1. Force the cards to load in a different order. I chose this route, and added the following to my /etc/modprobe.d/sound: 

  options snd-trident index=0
  options snd-usb-audio index=1

This forces my Trident card to be the default (card 0) and my USB microphone to be card 1.

2. Change the default card by editing /etc/asound.conf or ~/.asound.conf

Another problem is the OSS simultaneous incompatibility . Don't forget to disable any lines in /etc/modules.conf that correspond to the oss sound driver kernel modules.

More information

For more information, read the README.Debian files in the alsa-base and alsa-source packages or check out http://www.alsa-project.org and http://alsa.opensrc.org.

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