["Hardware"] - ["Sound"] - ?DebianSound


["ALSA"], the Advanced Linux Sound Architecture, is both a project and a body of software. The project was started because the ["OSS"] architecture is technically weak in some respects, and the free variant of OSS (see ["OSSFree"]) lacks some drivers available only in the commercial variant. For several years the ["ALSA"] software was developed separately from Linux. The drivers were added to the Linux codebase during the 2.5 development series and became the standard sound driver system in Linux 2.6.

["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 ?"AC3", etc.). ALSA provides efficient support for many applications (e.g., ["XMMS"]), is fully modularized, is [http://en.wikipedia.org/wiki/Symmetric_multiprocessing SMP] and thread-safe.

Applications written for OSS can be made to work with ALSA by means of either userspace emulation (using the [http://alsa.opensrc.org/index.php?page=alsa-oss aoss] program loader) or kernelspace emulation (the snd-*-oss drivers). However, you cannot use both ALSA and OSS drivers at the same time.

N.B. ALSA driver names always start with snd- .

Packages

Loading modules

Recent alsa-base packages are designed to "just" work with hotplug and discover. The alsa-base package does not load modules; instead, hotplug or discover detects the sound hardware and loads the right ALSA modules and then alsa-base takes care of setting usable mixer levels.

You can also run ["alsaconf"]. This program uses a different method of detecting hardware and if it thinks it has figured out what module is needed, it generates a /etc/modutils/sound or /etc/modprobe.d/sound file (depending on whether you are running Linux 2.4 or 2.6, respectively). With the latter file in place, the module in question will be loaded when the "snd" module is loaded. It suffices then to load the snd module in order to load the driver module for your specific hardware. To make use of this module loading mechanism you probably need to add "snd" to /etc/modules.

You can also try to detect and configure your sound card manually.

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.

ALSA and OSS

If your system is already configured to load OSS drivers for your sound card then look at your current module loader configuration files. There will be entries for the OSS modules which will give you clues about which chipsets your sound cards have. Don't forget to disable these entries before reconfiguring things to load ALSA modules.

If you don't unload all OSS modules then ALSA modules will not be able to initialise (or work properly) because the OSS driver will be futzing with the sound hardware that the ALSA driver needs to control. If you see a message about "sound card not detected" and you are sure you have the right ALSA driver, the presence of an OSS module could be the reason.

Test

Test the driver, using aplay, mplay or xmms for example

To test midi, you can use ["aplaymidi"].

Sharing a card among multiple processes

It is often desirable to be able to share a sound card among several processes running at the same time. This requires the ability to mix the sound outputs of those processes into a single stream.

If your cheap sound card doesn't support hardware mixing try the dmix plugin. This has been set up automatically since libasound2 version 1.0.10-2; in prior versions, look at /usr/share/doc/libasound2/examples/asound.conf_dmix to see how to enable DMIX in /etc/asound.conf (for all users) or ~.asoundrc (for your user). Also see [http://alsa.opensrc.org/index.php?page=AlsaSharing Alsa Wiki].

Troubleshooting

To see what indexes have been assigned to cards, run:

  cat /proc/asound/cards

The first card that ALSA finds is usually given index 0 and thus is usually the 'default' sound card. If you are unlucky then the first sound card found is one that it not suitable for playing system sounds. 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 ~/.asoundrc . More info on this Alsa [http://alsa.opensrc.org/FAQ026 FAQ]

Version

Look at /proc/asound/version.

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.

Please note with Debian Sarge my sound card is working right now but I still have NOTHING at /proc/asound though lsmod shows snd_intel8x0 and a whole bunch of other sound stuff.

See also: AlsaMidi.

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CategorySound