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User:SwifT/Wikified but not merged documents/ALSA guide
Introduction
What is ALSA?
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.
Installing ALSA
Before you proceed
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:
For ease of use/explanation, we assume the user has a PCI based sound card for the remainder of this guide.
We now proceed to find out details about the sound card.
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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/portage/make.conf before emerging any ALSA packages. Later in the guide, we will show you how to set up .
Configuring the kernel
Let us now configure the kernel to enable ALSA.
genkernel
users should now run genkernel --menuconfig all
and then follow the instructions in .'"`UNIQ--pre-00000003-QINU`"'
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The above example assumes that /usr/src/linux symlink points to the kernel sources you want to use. Please ensure the same before proceeding.
Now we will look at some of the options we will have to enable in the 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 section of this document. If you still like to have options built-in, ensure that you make changes to your config accordingly.
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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 and see if everything is working as it should.
Configuring/Testing ALSA
ALSA Utilities
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
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If you did not compile ALSA as modules, please proceed to the section. The rest of you need to configure ALSA. This is made very easy by the existence of the
alsaconf
tool provided by alsa-utils
.Configuration
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.
Please shut down any programs that might access the sound card while running
alsaconf
.To configure your sound card just type alsaconf
in a shell as root.
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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.
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.
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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.
Audio Group
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.
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Volume Check!
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.
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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.
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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.
Now, we shall unmute the channels, and set volume levels as needed.
Both Master and PCM need to be unmuted and set to audible volume levels if you want to hear some output on your speakers.
- To move between channels, use your left and right arrow keys. (<- & ->)
- To toggle mute, move to the specific channel, for example Master and press the m key on the keyboard.
- To increase and decrease the volume levels, use the up and down arrow keys respectively.
Be careful when setting your Bass and Treble values. 50 is usually a good number for both. Extremely high values of Bass may cause jarring on speakers that are not designed to handle them.
After you're all done, your ALSA Mixer should look similar to the one below. Note the 00 instead of the MM and also the volume levels for some optimum settings.
Sound Check!
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.
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And then play your favorite sound track...
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ALSA and USE
You can now add the alsa
use flag to /etc/portage/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.
Issues?
If for some reason you're unable to hear sound, the first thing to do would be to check your 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.
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The other most common issue users face is the dreaded "Unknown symbol in module" error. An example of the same is shown below.
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And when you take a look at dmesg
as suggested, you're quite likely to see:
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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!
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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.
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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.
Other things ALSA
Setting up MIDI support
First, check to make sure that you enabled the midi
USE flag in /etc/portage/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 for more information.
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You will need to copy over SoundFont (SF2) files from your sound card's driver CD or a Windows installation into /usr/share/sounds/sf2/ . For example a sound font file for the Creative SBLive! card would be 8MBGMSFX.SF2.
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.
/mnt paths mentioned in the code listing(s) below will not be the same in your machine. They are just an example. Please be careful to change the path to suit your machine.
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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.
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Virtual Synthesizers
If your sound card lacks a hardware synthesizer, you could use a virtual one like timidity++
. Installation is a breeze.
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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
.
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Don't forget to add timidity
to the default runlevel.
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You can now try out files.
Tools and Firmware
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
.
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Multiple sound cards
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.
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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.
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Plugins
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 .
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A big thank you to...
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.
References
Acknowledgements
We would like to thank the following authors and editors for their contributions to this guide:
- Shyam Mani
- Joshua Saddler
- Diego Pettenò