ALSA, which stands for Advanced Linux Sound Architecture, provides audio and MIDI (Musical Instrument Digital Interface) functionality to the Linux operating system. ALSA is the default sound subsystem in the 3.x and 2.6 kernels, thereby replacing OSS (Open Sound System), which was used in the 2.4 kernels.

ALSA's main features include efficient support for all types of audio interfaces ranging from consumer sound cards to professional sound equipment, fully modularized drivers, SMP and thread safety, backward compatibility with OSS and a user-space library alsa-lib to make application development a breeze.

First, you need to know what drivers your sound card uses. In most cases, sound cards (onboard and otherwise) are PCI based and lspci will help you in digging out the required information. Please emerge sys-apps/pciutils to get lspci, if you don't have it installed already. In case you have a USB sound card, lsusb from sys-apps/usbutils might be of help. For ISA cards, try using sys-apps/isapnptools. Also, the following pages may help users with ISA based sound cards:

• The ISAPNPTOOLS Page
• LinuxJournal PnP Article
• TLDP Sound HowTo

We now proceed to find out details about the sound card.

# lspci -v | grep -i audio
0000:00:0a.0 Multimedia audio controller: Creative Labs SB Live! EMU10k1 (rev 06)

We now know that the sound card on the machine is a Sound Blaster Live! and the card manufacturer is Creative Labs. Head over to the ALSA Soundcard Matrix page and select Creative Labs from the list. You will be taken to the Creative Labs matrix page where you can see that the SB Live! uses the emu10k1 module. That is the information we need for now. If you are interested in detailed information, you can click on the link next to the "Details" and that will take you to the emu10k1 specific page.

If you intend to use MIDI, then you should add midi to your USE flags in /etc/make.conf before emerging any ALSA packages. Later in the guide, we will show you how to set up MIDI support.

Let us now configure the kernel to enable ALSA.

# cd /usr/src/linux
# make menuconfig

Now we will look at some of the options we will have to enable in the 2.6 kernel to ensure proper ALSA support for our sound card.

Please note that for ease of use, all examples show ALSA built as modules. It is advisable to follow the same as it then allows the use of alsaconf which is a boon when you want to configure your card. Please do not skip the Configuration section of this document. If you still like to have options built-in, ensure that you make changes to your config accordingly.

Device Drivers  --->
   Sound  --->
   
(This needs to be enabled)
<M> Sound card support

(Make sure OSS is disabled)
Open Sound System   --->
   < > Open Sound System (DEPRECATED)

(Move one step back and enter ALSA)
Advanced Linux Sound Architecture  --->
   <M> Advanced Linux Sound Architecture
   (Select this if you want MIDI sequencing and routing)
   <M> Sequencer support
   (Old style /dev/mixer* and /dev/dsp* support. Recommended.)
   <M> OSS Mixer API
   <M> OSS PCM (digital audio) API 

(You now have a choice of devices to enable support for. Generally,
you will have one type of device and not more. If you have more than one
sound card, please enable them all here.)

(Mostly for testing and development purposes, not needed for normal
users unless you know what you are doing.)
Generic devices  --->
   
(For ISA Sound cards)
ISA devices   --->
(IF you had the Gravis, you would select this option)
   <M> Gravis UltraSound Extreme

(Move one level back and into PCI devices. Most sound cards today are
PCI devices)
PCI devices   --->
   (We now select the emu10k1 driver for our card)
   <M> Emu10k1 (SB Live!, Audigy, E-mu APS)
   (Or an Intel card would be)
   <M> Intel/SiS/nVidia/AMD/ALi AC97 Controller
   (Or if you have a VIA Card)
   <M> VIA 82C686A/B, 8233/8235 AC97 Controller

(Move one level back and select in case you have an USB sound card)
USB Devices   --->

Now that your options are set, you can (re)compile the kernel and ALSA support for your card should be functional once you reboot into the new kernel. Don't forget to update your GRUB configuration to use the newly built kernel. You can now proceed to ALSA Utilities and see if everything is working as it should.

alsa-utils forms an integral part of ALSA as it has a truckload of programs that are highly useful, including the ALSA Initscripts. Hence we strongly recommend that you install alsa-utils

# emerge alsa-utils

Recent versions of udev (>=udev-103) provide some degree of kernel-level autoconfiguration of your sound card. If possible, try to rely on just letting your kernel automatically setup your sound card for you. Otherwise, use alsaconf to configure your card, as shown below.

To configure your sound card just type alsaconf in a shell as root.

# alsaconf

You will now see a neat menu guided interface that will automatically probe your devices and try to find out your sound card. You will be asked to pick your sound card from a list. Once that's done, it will ask you permission to automatically make required changes to /etc/modprobe.d/alsa.conf. It will then adjust your volume settings to optimum levels, run update-modules and start the /etc/init.d/alsasound service. Once alsaconf exits, you can proceed with setting up the ALSA initscript.

We're now almost all setup. Whichever method you chose to install ALSA, you'll need to have something load your modules or initialize ALSA and restore your volume settings when your system comes up. The ALSA Initscript handles all of this for you and is called alsasound. Add it to the boot runlevel.

# rc-update add alsasound boot
 * alsasound added to runlevel boot
 * rc-update complete.

Next, just check the /etc/conf.d/alsasound file and ensure that SAVE_ON_STOP variable is set to yes. This saves your sound settings when you shutdown your system.

Before we move on to testing, there's one last important thing that needs to be setup. Rule of thumb in a *nix OS: Do not run as root unless needed. This applies here as well ;) How? Well, most of the times you should be logged in as a user and would like to listen to music or access your soundcard. For that to happen, you need to be in the "audio" group. At this point, we'll add users to the audio group, so that they won't have any issues when they want to access sound devices. We'll use gpasswd here and you need to be logged in as root for this to work.

(Substitute <username> with your user)
# gpasswd -a <username> audio 
Adding user <username> to group audio

We've completed all the setups and prerequisites, so let's fire up ALSA. If you ran alsaconf, you can skip this step, since alsaconf already does this for you.

# /etc/init.d/alsasound start

Now that the required things have been taken care of, we need to check up on the volume as in certain cases, it is muted. We use alsamixer for this purpose.

(Opens up a console program. Only required settings are shown)
# alsamixer

This is how the ALSA Mixer might look the first time you open it. Pay attention to the Master and PCM channels which both have an MM below them. That means they are muted. If you try to play anything with alsamixer in this state, you will not hear anything on your speakers.

Finally. Some music. If everything above is perfect, you should now be able to listen to some good music. A quick way to test is to use a command line tool like media-sound/madplay. You could also use something more well known like mpg123. If you are an ogg fan, you could use ogg123 provided by media-sound/vorbis-tools. Use any player you are comfortable with. As always, emerge what you need.

(Install the applications you want)
# emerge madplay mpg123
(To play .ogg files)
# emerge vorbis-tools

And then play your favorite sound track...

# madplay -v /mnt/shyam/Music/Paul\ Oakenfold\ -\ Dread\ Rock.mp3
MPEG Audio Decoder 0.15.2 (beta) - Copyright (C) 2000-2004 Robert Leslie et al.
          Title: Dread Rock
         Artist: Paul Oakenfold
          Album: Matrix Reloaded
           Year: 2003
          Genre: Soundtrack
                 Soundtrack
 00:04:19 Layer III, 160 kbps, 44100 Hz, joint stereo (MS), no CRC

# ogg123 Paul\ Oakenfold\ -\ Dread\ Rock.ogg
Audio Device:   Advanced Linux Sound Architecture (ALSA) output

Playing: Paul Oakenfold - Dread Rock.ogg
Ogg Vorbis stream: 2 channel, 44100 Hz
Genre: Soundtrack
Transcoded: mp3;160
Title: Dread Rock
Artist: Paul Oakenfold
Date: 2003
Album: Matrix Reloaded
Time: 00:11.31 [04:28.75] of 04:40.06  (200.6 kbps)  Output Buffer  96.9%

You can now add the alsa use flag to /etc/make.conf to ensure that your applications that support ALSA get built with it. Some architectures like x86 and amd64 have the flag enabled by default.

If for some reason you're unable to hear sound, the first thing to do would be to check your alsamixer settings. 80% of the issues lie with muted channels or low volume. Also check your Window Manager's sound applet and verify that volumes are set to audible levels.

/proc is your friend. And in this case, /proc/asound is your best friend. We shall just take a short look at how much info is made available to us there.

(First and foremost, if /proc/asound/cards shows your card, ALSA has
picked up your sound card fine.)
# cat /proc/asound/cards
0 [Live           ]: EMU10K1 - Sound Blaster Live!
                     Sound Blaster Live! (rev.6, serial:0x80271102) at 0xb800, irq 11

(This displays the current running ALSA version)
# cat /proc/asound/version
Advanced Linux Sound Architecture Driver Version 1.0.8 (Thu Jan 13 09:39:32 2005 UTC).

(ALSA OSS emulation details)
# cat /proc/asound/oss/sndstat
Sound Driver:3.8.1a-980706 (ALSA v1.0.8 emulation code)
Kernel: Linux airwolf.zion 2.6.11ac1 #2 Wed May 4 00:35:08 IST 2005 i686
Config options: 0

Installed drivers:
Type 10: ALSA emulation

Card config:
Sound Blaster Live! (rev.6, serial:0x80271102) at 0xb800, irq 11

Audio devices:
0: EMU10K1 (DUPLEX)

Synth devices: NOT ENABLED IN CONFIG

Midi devices:
0: EMU10K1 MPU-401 (UART)

Timers:
7: system timer

Mixers:
0: SigmaTel STAC9721/23

The other most common issue users face is the dreaded "Unknown symbol in module" error. An example of the same is shown below.

# /etc/init.d/alsasound start
 * Loading ALSA modules ...
 *   Loading: snd-card-0 ...                                              [ ok ]
 *   Loading: snd-pcm-oss ...
WARNING: Error inserting snd_mixer_oss
(/lib/modules/2.6.12-gentoo-r6/kernel/sound/core/oss/snd-mixer-oss.ko): Unknown
symbol in module, or unknown parameter (see dmesg) FATAL: Error inserting
snd_pcm_oss
(/lib/modules/2.6.12-gentoo-r6/kernel/sound/core/oss/snd-pcm-oss.ko): Unknown
symbol in module, or unknown parameter (see dmesg)                             
                                                                          [ !! ]
 *   Loading: snd-mixer-oss ...
FATAL: Error inserting snd_mixer_oss
(/lib/modules/2.6.12-gentoo-r6/kernel/sound/core/oss/snd-mixer-oss.ko): Unknown
symbol in module, or unknown parameter (see dmesg)                             
                                                                          [ !! ]
 *   Loading: snd-seq ...                                                 [ ok ]
 *   Loading: snd-emu10k1-synth ...                                       [ ok ]
 *   Loading: snd-seq-midi ...                                            [ ok ]
 * Restoring Mixer Levels ...                                             [ ok ]

And when you take a look at dmesg as suggested, you're quite likely to see:

(Only relevant portions are shown below)
# dmesg | less
ACPI: PCI Interrupt 0000:02:06.0[A] -> Link [APC3] -> GSI 18 (level, low) -> IRQ 209
snd_mixer_oss: Unknown symbol snd_unregister_oss_device
snd_mixer_oss: Unknown symbol snd_register_oss_device
snd_mixer_oss: Unknown symbol snd_mixer_oss_notify_callback
snd_mixer_oss: Unknown symbol snd_oss_info_register
snd_pcm_oss: Unknown symbol snd_unregister_oss_device
snd_pcm_oss: Unknown symbol snd_register_oss_device
snd_pcm_oss: Unknown symbol snd_mixer_oss_ioctl_card
snd_pcm_oss: Unknown symbol snd_oss_info_register
snd_mixer_oss: Unknown symbol snd_unregister_oss_device
snd_mixer_oss: Unknown symbol snd_register_oss_device
snd_mixer_oss: Unknown symbol snd_mixer_oss_notify_callback
snd_mixer_oss: Unknown symbol snd_oss_info_register

The above issue is caused when you switch from the alsa-driver to in-kernel ALSA because when you unmerge alsa-driver the module files are config protected and hence get left behind. So, when you switch to in-kernel drivers, running modprobe gives you a mix of alsa-driver and in-kernel modules thus causing the above errors.

The solution is quite easy. We just need to manually remove the problem causing directory after you unmerge alsa-driver. Be sure to remove the correct kernel version and not the current one!

# rm -rf /lib/modules/$(uname -r)/alsa-driver

Another reason for error messages similar to the ones above could be a file in /etc/modprobe.d supplying a device_mode parameter when it isn't required. Confirm that this is indeed the issue and find out which file is the culprit.

(Check dmesg to confirm)
# dmesg | grep device_mode
snd: Unknown parameter `device_mode'
(Now, to get to the source of the issue)
# grep device_mode /etc/modprobe.d/*

Usually it is a file called alsa with the line options snd device_mode=0666. Remove this line and restart the alsasound service and that should take care of this issue.

First, check to make sure that you enabled the midi USE flag in /etc/make.conf. If you didn't, go ahead and add it now. You will also need to re-emerge any ALSA packages that use the midi flag, such as alsa-lib and alsa-utils.

If your sound card is one of those that come with on-board MIDI synthesizers and you would like to listen to some .mid files, you have to install awesfx which is basically a set of utilities for controlling the AWE32 driver. We need to install it first. If you don't have a hardware synthesizer, you can use a virtual one. Please see the section on Virtual Synthesizers for more information.

# emerge awesfx

After copying over the Soundfont files, we can then play a midi file as shown. You can also add the asfxload command to /etc/conf.d/local.start, so that the sound font is loaded every time the system starts up.

(First, copy the Soundfont)
# cp /mnt/win2k/Program\ Files/CreativeSBLive2k/SFBank/8MBGMSFX.SF2 /usr/share/sounds/sf2/ 
(Or get it from your SoundBlaster CD)
# cp /mnt/cdrom/AUDIO/ENGLISH/SFBANK/8MBGMSFX.SF2 /usr/share/sounds/sf2/
(We load the specific Soundfont)
# asfxload /usr/share/sounds/sf2/8MBGMSFX.SF2

You can now play midi files using a program like aplaymidi. Run aplaymidi -l to get a list of available ports and then pick one to play the file on.

(Check open ports)
# aplaymidi -l
 Port    Client name                      Port name
 64:0    EMU10K1 MPU-401 (UART)           EMU10K1 MPU-401 (UART)
 65:0    Emu10k1 WaveTable                Emu10k1 Port 0
 65:1    Emu10k1 WaveTable                Emu10k1 Port 1
 65:2    Emu10k1 WaveTable                Emu10k1 Port 2
 65:3    Emu10k1 WaveTable                Emu10k1 Port 3
(Pick a port, and play a mid file)
#  aplaymidi --port=65:0 /mnt/shyam/music/midi/mi2.mid

If your sound card lacks a hardware synthesizer, you could use a virtual one like timidity++. Installation is a breeze.

# emerge timidity++

For timidity to play sounds, it needs a sound font. Fortunately, the ebuild will install some sound font packages for you. There are a few other font packages available in Portage, such as timidity-freepats and timidity-eawpatches. You can have multiple sound font configurations installed, and you can place your own in /usr/share/timidity/. To switch between different timidity configurations, you should use eselect.

# eselect timidity list
# eselect timidity set eawpatches

Don't forget to add timidity to the default runlevel.

# rc-update add timidity default
# /etc/init.d/timidity start

You can now try out Playing MIDI files.

Some specific sound cards can benefit from certain tools provided by the alsa-tools and alsa-firmware packages. You may install either with a simple emerge.

# emerge alsa-tools

You can have more than one sound card in your system simultaneously, provided that you have built ALSA as modules in your kernel. You just need to specify which should be started first in /etc/modprobe.d/alsa.conf. Your cards are identified by their driver names inside this file. 0 is the first card, 1 is the second, and so on. Here's an example for a system with two sound cards.

options snd-emu10k1 index=0
options snd-via82xx index=1

Or, if you have two cards that use the same driver, you specify them on the same line, using comma-separated numbers. Here's an example for a system with three sound cards, two of which are the same Intel High Definition Audio card.

options snd-ymfpci index=0
options snd-hda-intel index=1,2

You may want to install some plugins for extra functionality. alsa-plugins is a collection of useful plugins, which include: PulseAudio output, a sample rate converter, jack (a low-latency audio server), and an encoder that lets you output 6-channel audio through digital S/PDIF connections (both optical and coaxial). You can choose which of its plugins you want installed by adding their USE flags to /etc/portage/package.use.

# emerge -avt alsa-plugins

Everyone who contributed to the earlier version of the Gentoo ALSA Guide: Vincent Verleye, Grant Goodyear, Arcady Genkin, Jeremy Huddleston, John P. Davis, Sven Vermeulen, Benny Chuang, Tiemo Kieft and Erwin.

• The ALSA Project
• Linux Sound/MIDI Software