The Advanced Linux Sound Architecture (ALSA) is a project to improve the Linux sound subsystem by rewriting large chunks of it. It is anticipated that ALSA will make it into Linux kernel 2.6.x (or 3.x.x -- whichever comes first) as it becomes ready.

ALSA provides audio and MIDI functionality for Linux.

Quoted from http://www.alsa-project.org, ALSA has the following features:

• Efficient support for all types of audio interfaces, from consumer soundcards to professional multichannel audio interfaces.
• Fully modularized sound drivers.
• SMP and thread-safe design.
• User space library (alsa-lib) to simplify application programming and provide higher level functionality.
• Support for the older OSS API, providing binary compatibility for most OSS programs.

If your soundcard is supported by the Linux kernel sound system or the commercial OSS/4Front sound driver system, which can be found in all 2.4.x Linux kernels, you could just aswell build those modules for use with your soundcard. If you want this, just read through the Linux Sound HOWTO.

However, those OSS/4Front drivers have some limitations -- being commercial is one. ALSA is an attempt to go beyond these limitations and to do so in an open source fashion. ALSA is a fully GPL and LGPL'ed sound driver system, that provides a professional quality system for recording, playback, and MIDI sequencing.

ALSA tries to support as many (new) cards as possible by providing open-source drivers. However, some vendors may provide binary-only packages.

To know if your card is supported, you can find a Soundcard Matrix of supported and not-supported cards here: http://www.alsa-project.org/alsa-doc/.

Since we're still using 2.4.x kernel sources, we'll have to compile kernel modules and ALSA modules separately. People who are using a 2.5.x kernel can do this from within their kernel configuration, since the ALSA modules are included in the kernel sources and should be built there.

First we'll make sure that our kernel configuration is ready for use with ALSA. All you need in your kernel configuration is having Sound Card Support set to be built as a module (M). This will build soundcore.o.

Possibly, this will also work when you built Sound Card Support in the kernel (Y) instead of building it as a module (M). However, the official ALSA documentation suggests building it as a module, since ALSA will try loading it.

If you already have a working kernel configuration, make sure you remove all sound drivers (except for Sound Card Support). If you wish to do this without having to reboot, you could do like this:

# cd /usr/src/linux
# cp .config ~/
# make mrproper
# cp ~/.config .
# make menuconfig

Now select Sound Card Support as Module (M) and deselect all other sound drivers. Exit and say Y to save your kernel configuration. After that, build the modules:

# make dep clean
# make modules modules_install

Before installing your new modules, this last line will delete all your previous modules, even the ones from a previous ALSA installation.

This means, whenever you recompile your kernel later on, you MUST recompile alsa-driver.

However, there's no need to reinstall nvidia-kernel, the Nvidia drivers are in a separate directory in /lib/modules/*/video and won't get deleted by a make modules modules_install

Now it's time to install the ALSA drivers for your soundcard(s). If your soundcard is PCI, you can find out the name and type of your soundcard by looking at the output of /proc/pci

# grep audio /proc/pci

If you had a previous sound setup and there are still non-ALSA sound modules loaded, unload them now. Check with lsmod and use rmmod to unload all sound-related modules on your system.

We could simply do an emerge alsa-driver now, this would compile and install all ALSA sound drivers.

However, to save some time, lookup the Module Name of your soundcard(s) on the ALSA Soundcard Matrix by following the Details link in the Driver and Docs column in the row of the chipset of your soundcard. Mine is snd-emu10k1, since I have an SBlive! soundcard, with the EMU10K1 chipset. We'll set ALSA_CARDS environment to the value of the module name before emerging (but without the snd prefix), so emerge will only compile the drivers we need.

# env ALSA_CARDS='emu10k1' emerge alsa-driver 

After this, the ALSA modules should be installed on your system.

Let's start configuring now to get ALSA working properly. We'll need to edit some files, to let our system know about the freshly installed ALSA modules.

First, install alsa-utils on your system:

# emerge alsa-utils

Hereafter, we need to edit /etc/modules.d/alsa.

Check the ALSA portion at the bottom of the file. By tweaking this line you can specify the max number of soundcards you have (generally, just one).

# Set this to the correct number of cards.
options snd cards_limit=1

Now we'll specify the sounddriver(s) ALSA should use. In the same file, edit like this:

## and then run `modules-update' command.
## Read alsa-driver's INSTALL file in /usr/share/doc for more info.
##
##  ALSA portion
alias snd-card-0 snd-emu10k1
## If you have more than one, add:
## alias snd-card-1 snd-intel8x0
## alias snd-card-2 snd-ens1370
##  OSS/Free portion
## alias sound-slot-0 snd-card-0
## alias sound-slot-1 snd-card-1
##

If you have more than one soundcard, adjust the cards_limit value and add more snd-card aliases to the file. I don't have experience with this, but you can find examples for configurations with two or more soundcards in Chapter 6 of the ALSA Howto.

Last thing to do in this file, almost at the end, check if these lines are there and uncommented:

alias /dev/mixer snd-mixer-oss
alias /dev/dsp snd-pcm-oss
alias /dev/midi snd-seq-oss

Now double-check the file /etc/modules.d/alsa and when you're sure everyting is ok, run modules-update.

# modules-update

You should also verify that /etc/devfsd.conf has the alsa devices and permissions correctly registered.

# ALSA/OSS stuff
# Comment/change these if you want to change the permissions on
# the audio devices
LOOKUP          snd          MODLOAD ACTION snd
LOOKUP          dsp          MODLOAD
LOOKUP          mixer        MODLOAD
LOOKUP          midi         MODLOAD
REGISTER        sound/.*     PERMISSIONS root.audio 660
REGISTER        snd/.*       PERMISSIONS root.audio 660

First thing to do now, is to make ALSA startup at boottime. Like this:

# rc-update add alsasound boot

Note that the alsasound script should be added to the "boot" runlevel, not the "default" runlevel.

Since we're Linux users, we don't want to reboot. So we'll start the alsasound script manually.

# /etc/init.d/alsasound start

ALSA is running now. If everything is ok, you should be able to see the ALSA modules loaded when running lsmod. However, sound won't work yet, because the channels are still muted. We need amixer for this.

# amixer

You shouldn't get this, but if you get an error about "amixer: Mixer attach default error: No such file or directory", you should manually insmod snd-mixer-oss and snd-pcm-oss once. After that run amixer again.

# insmod snd-mixer-oss
# insmod snd-pcm-oss
# amixer

If you got this far, now unmute Master and PCM channels. Some hardware even requires you to unmute the center channel or even the surround channel.

# amixer set Master 100 unmute
# amixer set PCM 100 unmute
Only if the above doesn't succeed on its own:
# amixer set Center 100 unmute
# amixer set Surround 100 unmute
Test the sound:
# aplay $KDEDIR/share/sounds/pop.wav (pop.wav is part of KDE)

You may want to emerge alsa-xmms as that will provide ALSA support for XMMS.

When you ever rebuild your kernel, or upgrade to another kernel, you'll have to rebuild the ALSA modules.

Although you might have installed alsa-driver, alsa-libs and alsa-utils, only the first will have to be installed again, since it will put the alsa modules in /lib/modules/*/kernel/sound/pci/.

# emerge alsa-driver

You won't have to edit this file for use with ALSA. After our rc-update add alsasound boot, our system will load the correct modules at startup.

It's not necessary to add snd-pcm-oss or snd-mixer-oss in this file. Check the this FAQ for more info.

You could check these for additional info:

• The Gentoo Linux Desktop Configuration Guide
• ALSA Project Homepage
• ALSA Users Documentation
• ALSA Howto's and FAQ's
• Linux Sound HOWTO
• Sound and MIDI Software For Linux