Difference between revisions of "Advanced Linux Sound Architecture"

Revision as of 22:20, 31 March 2013

zh-CN:Advanced Linux Sound Architecture The Advanced Linux Sound Architecture (ALSA) is a Linux kernel component which replaced the original Open Sound System (OSSv3) for providing device drivers for sound cards. Besides the sound device drivers, ALSA also bundles a user space library for application developers who want to use driver features with a higher level API than direct interaction with the kernel drivers.

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Installation

ALSA is included in the default Arch kernel as a set of modules, so installing it is not necessary.

udev will automatically probe your hardware at boot, loading the corresponding kernel module for your audio card. Therefore, your sound should already be working, but upstream sources mute all channels by default.

Users with a local login (at a virtual terminal or a display manager) have permission to play audio and change mixer levels. To allow this for a remote login, the user has to be added to the audio group. Membership in the audio group also allows direct access to devices, which can lead to applications grabbing exclusive output (breaking software mixing) and breaks fast-user-switching, and multiseat. Therefore, adding a user to the audio group is not recommended, unless you specifically need to[1].

User-space utilities

From official repositories:

• Install the alsa-utils package which contains the alsamixer user-space tool, which allows for configuration of the sound device from the console or terminal.
• Install the alsa-oss package if you want OSS applications to work with dmix (software mixing).

• Install the alsa-plugins package if you want high quality resampling, upmixing/downmixing and other advanced features.

Unmuting the channels

The current version of ALSA installs with all channels muted by default. You will need to unmute the channels manually.

It is easiest to use alsamixer ncurses UI to accomplish this:

$ alsamixer

Alternatively, use amixer from the command-line:

$ amixer sset Master unmute

m In alsamixer, the MM label below a channel indicates that the channel is muted, and 00 indicates that it is open.

Scroll to the Master and PCM channels with the Template:Keypress and Template:Keypress keys and unmute them by pressing the Template:Keypress key. Use the Template:Keypress key to increase the volume and obtain a value of 0 dB gain. The gain can be found in the upper left next to the Item: field. Higher values of gain will produce distorted sound.

To get full 5.1 or 7.1 surround sound you likely need to unmute other channels such as Front, Surround, Center, LFE (subwoofer) and Side (these are the names of the channels with Intel HD Audio, they may vary with different hardware). Please take note that this will not automatically upmix stereo sources (like most music). In order to accomplish that, see #Upmixing/Downmixing.

To enable your microphone, switch to the Capture tab with Template:Keypress and enable a channel with Template:Keypress.

Leave alsamixer by pressing Template:Keypress.

Next, test to see if sound works:

$ speaker-test -c 2

Change -c to fit your speaker setup. Use -c 8 for 7.1, for instance:

$ speaker-test -c 8

If it does not work, proceed to #Configuration and then #Troubleshooting to solve your problems.

The alsa-utils package includes alsa-restore.service and alsa-store.service, which are preconfigured to run at boot and shutdown respectively.

Configuration

No sound in virtualbox

If you experience problems with virtualbox, the following command might be helpful:

$ alsactl init

Found hardware: "ICH" "SigmaTel STAC9700,83,84" "AC97a:83847600" "0x8086" "0x0000"
Hardware is initialized using a generic method

You might need to activate the ALSA output in your audio software as well.

Set the default sound card

If your sound card order changes on boot, you can specify their order in any file ending with .conf in /etc/modprobe.d (/etc/modprobe.d/alsa-base.conf is suggested). For example, if you want your mia sound card to be #0:

/etc/modprobe.d/alsa-base.conf

options snd slots=snd_mia,snd_hda_intel
options snd_mia index=0
options snd_hda_intel index=1

lsmod | grep snd to get a devices list

snd_mia and snd_hda_intel are the modules used by the respective cards. This configuration assumes you have one mia sound card and one card using snd_hda_intel (e.g. onboard).

You can also provide an index of -2 to instruct ALSA to never use a card as the primary one. Distributions such as Linux Mint and Ubuntu use the following settings to avoid USB and other "abnormal" drivers from getting index 0:

/etc/modprobe.d/alsa-base.conf

options bt87x index=-2
options cx88_alsa index=-2
options saa7134-alsa index=-2
options snd-atiixp-modem index=-2
options snd-intel8x0m index=-2
options snd-via82xx-modem index=-2
options snd-usb-audio index=-2
options snd-usb-caiaq index=-2
options snd-usb-ua101 index=-2
options snd-usb-us122l index=-2
options snd-usb-usx2y index=-2
# Keep snd-pcsp from being loaded as first soundcard
options snd-pcsp index=-2
# Keep snd-usb-audio from beeing loaded as first soundcard
options snd-usb-audio index=-2

These changes require a system reboot.

First you will have to find out the card and device id that you want to set as the default by running aplay -l:

$ aplay -l

**** List of PLAYBACK Hardware Devices ****
card 0: Intel [HDA Intel], device 0: CONEXANT Analog [CONEXANT Analog]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 0: Intel [HDA Intel], device 1: Conexant Digital [Conexant Digital]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 1: JamLab [JamLab], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
card 2: Audio [Altec Lansing XT1 - USB Audio], device 0: USB Audio [USB Audio]
  Subdevices: 1/1
  Subdevice #0: subdevice #0

For example, the last entry in this list has the card ID 2 and the device ID 0. To set this card as the default, you can either use the system-wide file /etc/asound.conf or the user-specific file ~/.asoundrc. You may have to create the file if it does not exist. Then insert the following options with the corresponding card and device id.

~/.asoundrc

defaults.pcm.card 2
defaults.pcm.device 0
defaults.ctl.card 2

The 'pcm' options affect which card and device will be used for audio playback while the 'ctl' option affects which card is used by control utilities like alsamixer .

The changes should take effect as soon as you (re-)start an application (mplayer etc.).

Making sure the sound modules are loaded

You can assume that udev will autodetect your sound properly. You can check this with the command

$ lsmod | grep '^snd' | column -t

snd_hda_codec_hdmi     22378   4
snd_hda_codec_realtek  294191  1
snd_hda_intel          21738   1
snd_hda_codec          73739   3  snd_hda_codec_hdmi,snd_hda_codec_realtek,snd_hda_intel
snd_hwdep              6134    1  snd_hda_codec
snd_pcm                71032   3  snd_hda_codec_hdmi,snd_hda_intel,snd_hda_codec
snd_timer              18992   1  snd_pcm
snd                    55132   9  snd_hda_codec_hdmi,snd_hda_codec_realtek,snd_hda_intel,snd_hda_codec,snd_hwdep,snd_pcm,snd_timer
snd_page_alloc         7017    2  snd_hda_intel,snd_pcm

If the output looks similar, your sound drivers have been successfully autodetected.

You might also want to check the directory /dev/snd/ for the right device files:

$ ls -l /dev/snd

total 0
crw-rw----  1 root audio 116,  0 Apr  8 14:17 controlC0
crw-rw----  1 root audio 116, 32 Apr  8 14:17 controlC1
crw-rw----  1 root audio 116, 24 Apr  8 14:17 pcmC0D0c
crw-rw----  1 root audio 116, 16 Apr  8 14:17 pcmC0D0p
crw-rw----  1 root audio 116, 25 Apr  8 14:17 pcmC0D1c
crw-rw----  1 root audio 116, 56 Apr  8 14:17 pcmC1D0c
crw-rw----  1 root audio 116, 48 Apr  8 14:17 pcmC1D0p
crw-rw----  1 root audio 116,  1 Apr  8 14:17 seq
crw-rw----  1 root audio 116, 33 Apr  8 14:17 timer

If you have at least the devices controlC0 and pcmC0D0p or similar, then your sound modules have been detected and loaded properly.

If this is not the case, your sound modules have not been detected properly. To solve this, you can try loading the modules manually:

• Locate the module for your sound card: ALSA Soundcard Matrix The module will be prefixed with 'snd-' (for example: snd-via82xx).
• Load the module.
• Check for the device files in /dev/snd (see above) and/or try if alsamixer or amixer have reasonable output.
• Configure snd-NAME-OF-MODULE and snd-pcm-oss to load at boot.

Getting SPDIF Output

(from gralves from the Gentoo forums)

• In GNOME Volume Control, under the Options tab, change the IEC958 to PCM. This option can be enabled in the preferences.
• If you do not have GNOME Volume Control installed,
  • Edit /var/lib/alsa/asound.state. This file is where alsasound stores your mixer settings.
  • Find a line that says: 'IEC958 Playback Switch'. Near it you will find a line saying value:false. Change it to value:true.
  • Now find this line: 'IEC958 Playback AC97-SPSA'. Change its value to 0.
  • Restart ALSA.

Alternative way to enable SPDIF output automatically on login (tested on SoundBlaster Audigy):

• add following lines to /etc/rc.local:

 # Use COAX-digital output
 amixer set 'IEC958 Optical' 100 unmute
 amixer set 'Audigy Analog/Digital Output Jack' on

You can see the name of your card's digital output with:

 $ amixer scontrols

System-Wide Equalizer

Using AlsaEqual (provides UI)

Install alsaequal^AUR from the AUR.

After installing the package, insert the following into your ALSA configuration file (~/.asoundrc or /etc/asound.conf):

ctl.equal {
 type equal;
}

pcm.plugequal {
  type equal;
  # Modify the line below if you do not
  # want to use sound card 0.
  #slave.pcm "plughw:0,0";
  #by default we want to play from more sources at time:
  slave.pcm "plug:dmix";
}
#pcm.equal {
  # If you do not want the equalizer to be your
  # default soundcard comment the following
  # line and uncomment the above line. (You can
  # choose it as the output device by addressing
  # it with specific apps,eg mpg123 -a equal 06.Back_In_Black.mp3)
pcm.!default {
  type plug;
  slave.pcm plugequal;
}

And you are ready to change your equalizer using command

$ alsamixer -D equal

Note that configuration file is different for each user (until not specified else) it is saved in ~/.alsaequal.bin. so if you want to use AlsaEqual with mpd or another software running under different user, you can configure it using

# su mpd -c 'alsamixer -D equal'

or for example, you can make a symlink to your .alsaequal.bin in his home...

Managing AlsaEqual States

Install alsaequal-mgr from Xyne's repos or the AUR.

Configure the equalizer as usual with

$alsamixer -D equal

When you are satisfied with the state, you may give it a name ("foo" in this example) and save it:

$alsaequal-mgr save foo

The state "foo" can then be restored at a later time with

$alsaequal-mgr load foo

You can thus create different equalizer states for games, movies, music genres, VoIP apps, etc. and reload them as necessary.

See the project page and the help message for more options.

Using mbeq

Install the alsa-plugins, ladspa and swh-plugins packages if you do not already have them.

• If you have not already created either an ~/.asoundrc or a /etc/asound.conf file, then create either one and insert the following:

/etc/asound.conf

pcm.eq {
  type ladspa

  # The output from the EQ can either go direct to a hardware device
  # (if you have a hardware mixer, e.g. SBLive/Audigy) or it can go
  # to the software mixer shown here.
  #slave.pcm "plughw:0,0"
  slave.pcm "plug:dmix"

  # Sometimes you may need to specify the path to the plugins,
  # especially if you have just installed them.  Once you have logged
  # out/restarted this should not be necessary, but if you get errors
  # about being unable to find plugins, try uncommenting this.
  #path "/usr/lib/ladspa"

  plugins [
    {
      label mbeq
      id 1197
      input {
        #this setting is here by example, edit to your own taste
        #bands: 50hz, 100hz, 156hz, 220hz, 311hz, 440hz, 622hz, 880hz, 1250hz, 1750hz, 25000hz,
        #50000hz, 10000hz, 20000hz
        controls [ -5 -5 -5 -5 -5 -10 -20 -15 -10 -10 -10 -10 -10 -3 -2 ]
      }
    }
  ]
 }

 # Redirect the default device to go via the EQ - you may want to do
 # this last, once you are sure everything is working.  Otherwise all
 # your audio programs will break/crash if something has gone wrong.

 pcm.!default {
  type plug
  slave.pcm "eq"
 }

 # Redirect the OSS emulation through the EQ too (when programs are running through "aoss")

 pcm.dsp0 {
  type plug
  slave.pcm "eq"
 }

• You should be good to go (if not, ask in the forum).

High quality resampling

When software mixing is enabled, ALSA is forced to resample everything to the same frequency (48000 by default when supported). dmix uses a poor resampling algorithm which produces noticeable sound quality loss.

Install alsa-plugins and libsamplerate.

Change the default rate converter to libsamplerate:

/etc/asound.conf

defaults.pcm.rate_converter "samplerate_best"

or

~/.asoundrc

defaults.pcm.rate_converter "samplerate_best"

samplerate_best offers the best sound quality, but you need a decent CPU to be able to use it as it requires a lot of CPU cycles for real-time resampling. There are other algorithms available (samplerate, etc.) but they may not provide much of an improvement over the default resampler.

Upmixing/Downmixing

Upmixing

In order for stereo sources like music to be able to saturate a 5.1 or 7.1 sound system, you need to use upmixing. In darker days this used to be tricky and error prone but nowadays plugins exist to easily take care of this task. Thus, install alsa-plugins.

Then add the following to your ALSA configuration file of choice (either /etc/asound.conf or ~/.asoundrc):

pcm.upmix71 {
    type upmix
    slave.pcm "surround71"
    delay 15
    channels 8
}

You can easily change this example for 7.1 upmixing to 5.1 or 4.0.

This adds a new pcm that you can use for upmixing. If you want all sound sources to go through this pcm, add it as a default below the previous definition like so:

pcm.!default "plug:upmix71"

The plugin automatically allows multiple sources to play through it without problems so setting is as a default is actually a safe choice. If this is not working, you have to setup your own dmixer for the upmixing PCM like this:

pcm.dmix6 {
    type asym
    playback.pcm {
        type dmix
        ipc_key 567829
        slave {
            pcm "hw:0,0"
            channels 6
        }
    }
}

and use "dmix6" instead of "surround71". If you experience skipping or distorted sound, consider increasing the buffer_size (to 32768, for example) or use a high quality resampler.

Downmixing

If you want to downmix sources to stereo because you, for instance, want to watch a movie with 5.1 sound on a stereo system, you need to use the vdownmix plugin that alsa provides in the same package.

Again, in your configuration file, add this:

pcm.!surround51 {
    type vdownmix
    slave.pcm "default"
}
pcm.!surround40 {
    type vdownmix
    slave.pcm "default"
}

Mixing

Software mixing (dmix)

If that does not work however, it is a matter of simply creating a .asoundrc file in your home folder with the following contents.

pcm.dsp {
    type plug
    slave.pcm "dmix"
}

This should enable software mixing and allows more than one application to make use of the soundcard.

For a digital sound output such as S/PDIF, the ALSA package still does not enable dmix by default. Thus, the dmix configuration above can be used to enable dmix for S/PDIF devices.

See #Troubleshooting for common problems and solutions.

Hardware mixing

Support

If you have an audio chipset that supports mixing in hardware, then no configuration is necessary. Almost every onboard audio chipset does not support hardware mixing, and requires mixing to be done in software (see above). Many sound cards do support hardware mixing, and the ones best supported on Linux are listed below:

• Creative SoundBlaster Live! (5.1 model)
• Creative SoundBlaster Audigy (some models)
• Creative SoundBlaster Audidy 2 (ZS models)
• Creative SoundBlaster Audigy 4 (Pro models)

Fixes

If you are using 64-bit Arch and the Intel Corporation 82801I (ICH9 Family) HD Audio Controller (rev 02), you can get sound working for Enemy Territory with the following:

echo "et.x86 0 0 direct" > /proc/asound/card0/pcm0p/oss
echo "et.x86 0 0 disable" > /proc/asound/card0/pcm0c/oss

Troubleshooting

Sound Skipping While Using Dynamic Frequency Scaling

Some combinations of ALSA drivers and chipsets may cause audio from all sources to skip when used in combination with a dynamic frequency scaling governor such as ondemand or conservative. Currently, the solution is to switch back to the performance governor.

Refer to the CPU Frequency Scaling for more information.

Problems with Availability to Only One User at a Time

You might find that only one user can use the dmixer at a time. This is probably ok for most, but for those who run mpd as a separate user this poses a problem. When mpd is playing a normal user cannot play sounds though the dmixer. While it's quite possible to just run mpd under a user's login account, another solution has been found. Adding the line ipc_key_add_uid 0 to the pcm.dmixer block disables this locking. The following is a snippet of the asound.conf, the rest is the same as above.

...
pcm.dmixer {
 type dmix
 ipc_key 1024
 ipc_key_add_uid 0
 ipc_perm 0660
slave {
...

Simultaneous Playback Problems

If you are having problems with simultaneous playback, and if PulseAudio is installed (i.e. by GNOME), its default configuration is set to "hijack" the soundcard. Some users of ALSA may not want to use PulseAudio and are quite content with their current ALSA settings. One fix is to edit /etc/asound.conf and comment out the following lines:

# Use PulseAudio by default
#pcm.!default {
#  type pulse
#  fallback "sysdefault"
#  hint {
#    show on
#    description "Default ALSA Output (currently PulseAudio Sound Server)"
#  }
#}

Commenting the following out also may help:

#ctl.!default {
#  type pulse
#  fallback "sysdefault"
#}

This may be a much simpler solution than completely uninstalling PulseAudio.

Effectively, here is an example of a working /etc/asound.conf:

pcm.dmixer {
        type dmix
        ipc_key 1024
        ipc_key_add_uid 0
        ipc_perm 0660
}
pcm.dsp {
        type plug
        slave.pcm "dmix"
}

Random Lack of Sound on Startup

If you randomly have no sound on startup, it may be because your system has multiple sound cards, and their order may sometimes change on startup. If this is the case, try setting the default sound card.

If you use mpd and the configuration tips above do not work for you, try reading this instead.

Specific Program Problems

For other programs who insist on their own audio setup, eg, XMMS or Mplayer, you would need to set their specific options.

For mplayer, open up ~/.mplayer/config (or /etc/mplayer/mplayer.conf for global setting) and add the following line:

ao=alsa

For XMMS/Beep Media Player, go into their options and make sure the sound driver is set to Alsa, not oss.

To do this in XMMS:

• Open XMMS
  • Options -> preferences.
  • Choose the Alsa output plugin.

For applications which do not provide a ALSA output, you can use aoss from the alsa-oss package. To use aoss, when you run the program, prefix it with aoss, eg:

aoss realplay

pcm.!default{ ... } doesnt work for me anymore. but this does:

 pcm.default pcm.dmixer

Model Settings

Although Alsa detects your soundcard through the BIOS at times Alsa may not be able to recognize your model type. The soundcard chip can be found in alsamixer (e.g. ALC662) and the model can be set in /etc/modprobe.d/modprobe.conf or /etc/modprobe.d/sound.conf. For example:

options snd-hda-intel model=MODEL

There are other model settings too. For most cases Alsa defaults will do. If you want to look at more specific settings for your soundcard take a look at the Alsa Soundcard List find your model, then Details, then look at the "Setting up modprobe..." section. Enter these values in /etc/modprobe.d/modprobe.conf. For example, for an Intel AC97 audio:

# ALSA portion
alias char-major-116 snd
alias snd-card-0 snd-intel8x0
# module options should go here

# OSS/Free portion
alias char-major-14 soundcore
alias sound-slot-0 snd-card-0

# card #1
alias sound-service-0-0 snd-mixer-oss
alias sound-service-0-1 snd-seq-oss
alias sound-service-0-3 snd-pcm-oss
alias sound-service-0-8 snd-seq-oss
alias sound-service-0-12 snd-pcm-oss

Conflicting PC Speaker

If you are sure nothing is muted, that your drivers are installed correctly, and that your volume is right, but you still do not hear anything, then try adding the following line to /etc/modprobe.d/modprobe.conf:

options snd-NAME-OF-MODULE ac97_quirk=0

The above fix has been observed to work with via82xx

options snd-NAME-OF-MODULE ac97_quirk=1

The above fix has been reported to work with snd_intel8x0

No Microphone Input

In alsamixer, make sure that all the volume levels are up under recording, and that CAPTURE is toggled active on the microphone (e.g. Mic, Internal Mic) and/or on Capture (in alsamixer, select these items and press space). Try making positive Mic Boost and raising Capture and Digital levels higher; this make make static or distortion, but then you can adjust them back down once you are hearing something when you record

As the pulseaudio wrapper is shown as "default" in alsamixer, you may have to press F6 to select your actual soundcard first. You may also need to enable and increase the volume of Line-in in the Playback section.

To test the microphone, run these commands (see arecord's man page for further information):

 arecord -d 5 test-mic.wav
 aplay test-mic.wav

If all fails, you may want to eliminate hardware failure by testing the microphone with a different device.

For at least some computers, muting a microphone (MM) simply means its input does not go immediately to the speakers. It still receives input.

Many Dell laptops need "-dmic" to be appended to the model name in /etc/modprobe.d/modprobe.conf:

 options snd-hda-intel model=dell-m6-dmic

Some programs use try to use OSS as the main input software. Add the following lines to /etc/modprobe.d/modprobe.conf to prevent OSS modules from being loaded:

blacklist snd_pcm_oss
blacklist snd_mixer_oss
blacklist snd_seq_oss

See also:

• http://www.alsa-project.org/main/index.php/SoundcardTesting
• http://alsa.opensrc.org/Record_from_mic

Setting the default Microphone/Capture Device

Some applications (Pidgin, Adobe Flash) do not provide an option to change the capture device. It becomes a problem if your microphone is on a separate device (e.g. USB webcam or microphone) than your internal sound card. To change only the default capture device, leaving the default playback device as is, you can modify your ~/.asoundrc file to include the following:

pcm.usb
{
    type hw
    card U0x46d0x81d
}

pcm.!default
{
    type asym
    playback.pcm
    {
        type plug
        slave.pcm "dmix"
    }
    capture.pcm
    {
        type plug
        slave.pcm "usb"
    }
}

Replace "U0x46d0x81d" with your capture device's card name in ALSA. You can use arecord -L to list all the capture devices detected by ALSA.

Internal Microphone not working

First make sure all the volume levels are up under recording in alsamixer. In my case adding the following option to /etc/sound.conf and reloading the snd-* module produced a new volume setting called Capture which was capturing for the internal mic. For eg, for snd-hda-intel add

 options snd-hda-intel enable_msi=1

Then reload the module (as below), up the recording volume of Capture and then test.

# rmmod snd-hda-intel && modprobe snd-hda-intel

No Sound with Onboard Intel Sound Card

There may be a problem with two conflicting modules loaded, namely snd_intel8x0 and snd_intel8x0m. In this case, blacklist snd_intel8x0m:

/etc/modprobe.d/modprobe.conf

blacklist snd_intel8x0m

Muting the "External Amplifier" in alsamixer or amixer may also help. See the ALSA wiki.

Unmuting the "Mix" setting in the mixer might help, also.

No Headphone Sound with Onboard Intel Sound Card

With Intel Corporation 82801 I (ICH9 Family) HD Audio Controller on laptop, you may need to add this line to modprobe or sound.conf:

options snd-hda-intel model=$model

Where $model is any one of the following (in order of possibility to work, but not merit):

• dell-vostro
• olpc-xo-1_5
• laptop
• dell-m6
• laptop-hpsense

Note: It may be necessary to put this "options" line below (after) any "alias" lines about your card.

You can see all the available models in the kernel documentation. For example here, but check that it is the correct version of that document for your kernel version.

A list of available models is also available here. To know your chip name type the following command (with * being corrected to match your files). Note that some chips could have been renamed and do not directly match the available ones in the file.

cat /proc/asound/card*/codec* | grep Codec

Note that there is a high chance none of the input devices (all internal and external mics) will work if you choose to do this, so it is either your headphones or your mic. Please report to ALSA if you are affected by this bug.

And also, if you have problems getting beeps to work (pcspkr):

options snd-hda-intel model=$model enable=1 index=0

No sound when S/PDIF video card is installed

Discover available modules and their order:

$ cat /proc/asound/modules
0 snd_hda_intel
1 snd_ca0106

Disable the undesired video card audio codec in /etc/modprobe.d/modprobe.conf:

# /etc/modprobe.d/modprobe.conf
#
install snd_hda_intel /bin/false

If both devices use the same module, it might be possible to disable one of them in the BIOS.

Poor sound quality or clipping

If you experience poor sound quality, try setting the PCM volume (in alsamixer) to a level such that gain is 0.

If snd-usb-audio driver has been loaded, you could try to enable softvol in /etc/asound.conf file. Example configuration for the first audio device:

 pcm.!default {
   type plug
   slave.pcm "softvol"
 }
 pcm.dmixer {
      type dmix
      ipc_key 1024
      slave {
          pcm "hw:0"
          period_time 0
          period_size 4096
          buffer_size 131072
          rate 50000
      }
      bindings {
          0 0
          1 1
      }
 }
 pcm.dsnooper {
      type dsnoop
      ipc_key 1024
      slave {
          pcm "hw:0"
          channels 2
          period_time 0
          period_size 4096
          buffer_size 131072
          rate 50000
      }
      bindings {
          0 0
          1 1
      }
 }
 pcm.softvol {
      type softvol
      slave { pcm "dmixer" }
      control {
          name "Master"
          card 0
      }
 }
 ctl.!default {
   type hw
   card 0
 }
 ctl.softvol {
   type hw
   card 0
 }
 ctl.dmixer {
   type hw
   card 0
 }

Pops When Starting and Stopping Playback

Some modules (e.g. snd_ac97_codec and snd_hda_intel) can power off your sound card when not in use. This can make an audible noise (like a crack/pop/scratch) when turning on/off your sound card. Sometimes even when move the slider volume, or open and close windows (KDE4). If you find this annoying try modinfo snd_MY_MODULE, and look for a module option that adjusts or disables this feature.

Example: to disable the power saving mode and solve cracking sound trough speakers problem, using snd_hda_intel add in /etc/modprobe.d/modprobe.conf

options snd_hda_intel power_save=0

or

options snd_hda_intel power_save=0 power_save_controller=N

You can also try it with modprobe snd_hda_intel power_save=0 before.

You may also have to unmute the 'Line' ALSA channel for this to work. Any value will do (other than '0' or something too high).

Example: on an onboard VIA VT1708S (using the snd_hda_intel module) these cracks occured even though 'power_save' was set to 0. Unmuting the 'Line' channel and setting a value of '1' solved the problem.

Source: https://www.kernel.org/doc/Documentation/sound/alsa/powersave.txt

If you use a laptop, pm-utils will change power_save back to 1 when you go onto battery power even if you disable power saving in /etc/modprobe.d. Disable this for pm-utils by disabling the script that makes the change (see Disabling a hook for more information):

# touch /etc/pm/power.d/intel-audio-powersave

S/PDIF Output Does Not Work

If the optical/coaxial digital output of your motherboard/sound card is not working or stopped working, and have already enabled and unmuted it in alsamixer, try running

# iecset audio on

as root.

You can also put this command in rc.local as it sometimes it may stop working after a reboot.

HDMI Output Does Not Work

If the HDMI output of your motherboard/sound card is not working or stopped working, and have already enabled and unmuted it in alsamixer, try the following.

Query for Playback Devices:

 $ aplay -l
 **** List of PLAYBACK Hardware Devices ****
 card 0: NVidia [HDA NVidia], device 0: ALC1200 Analog [ALC1200 Analog]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
 card 0: NVidia [HDA NVidia], device 1: ALC1200 Digital [ALC1200 Digital]
   Subdevices: 1/1
   Subdevice #0: subdevice #0
 card 0: NVidia [HDA NVidia], device 3: NVIDIA HDMI [NVIDIA HDMI]
   Subdevices: 0/1
   Subdevice #0: subdevice #0

Now that we have the info for the HDMI device, try a test, In the example below, 0 is the card number and 3 is the device number.

 $ aplay -D plughw:0,3 /usr/share/sounds/alsa/Front_Center.wav

If aplay does not output any errors, but still no sound is heared, "reboot" the receiver, monitor or tv set. Since the HDMI interface executes a handshake on connection, it might have noticed before that there was no audio stream embedded, and disabled audio decoding. In particular, if you are using a standalone window manager (don’t know about Gnome or KDE), you may need to have some sound playing while plugging in the HDMI cable.

If the test is successful, create or edit your ~/.asoundrc file to set HDMI as the default audio device.

~/.asoundrc

pcm.!default {
  type hw
  card 0
  device 3
}

Or you above config does not work try:

~/.asoundrc

defaults.pcm.card 0
defaults.pcm.device 3
defaults.ctl.card 0

HDMI Multi-channel PCM output does not work (Intel)

As of Linux 3.1 multi-channel PCM output through HDMI with a Intel card (Intel Eaglelake, IbexPeak/Ironlake,SandyBridge/CougarPoint and IvyBridge/PantherPoint) is not yet supported. Support for it has been recently added and expected to be available in Linux 3.2. To make it work in Linux 3.1 you need to apply the following patches:

• drm: support routines for HDMI/DP ELD
• drm/i915: pass ELD to HDMI/DP audio driver

HP TX2500

Add these 2 lines into /etc/modprobe.d/modprobe.conf:

options snd-cmipci mpu_port=0x330 fm_port=0x388
options snd-hda-intel index=0 model=toshiba position_fix=1

options snd-hda-intel model=hp (works for tx2000cto)

Skipping Sound When Playing MP3

If you have sound skipping when playing MP3 files and you have more then 2 speakers attached to your computer (i.e. > 2 speaker system), run alsamixer and disable the channels for the speakers that you DO NOT have (i.e. do not enable the sound for the center speaker if you do not have a center speaker.

Using a USB Headset and External USB Sound Cards

If you are using a USB headset with ALSA you can try using asoundconf^AUR (currently only available from the AUR) to set the headset as the primary sound output. Before running make sure you have usb audio module enabled (modprobe snd-usb-audio).

# asoundconf is-active
# asoundconf list
# asoundconf set-default-card <chosen soundcard>

Crackling sound with USB devices

If you experience crackling sound on USB devices, you can try tuning the snd-usb-audio for minimal latency.

Add this to your /etc/modprobe.d/modprobe.conf:

options snd-usb-audio nrpacks=1

source: http://alsa.opensrc.org/Usb-audio#Tuning_USB_devices_for_minimal_latencies

Hot-plugging a USB Sound Card

In order to automatically make a USB Sound Card the primary output device, when the card is plugged in, you can use the following udev rules (e.g. add the following two lines to /etc/udev/rules.d/00-local.rules and reboot).

KERNEL=="pcmC[D0-9cp]*", ACTION=="add", PROGRAM="/bin/sh -c 'K=%k; K=$${K#pcmC}; K=$${K%%D*}; echo defaults.ctl.card $$K > /etc/asound.conf; echo defaults.pcm.card $$K >>/etc/asound.conf'"
KERNEL=="pcmC[D0-9cp]*", ACTION=="remove", PROGRAM="/bin/sh -c 'echo defaults.ctl.card 0 > /etc/asound.conf; echo defaults.pcm.card 0 >>/etc/asound.conf'"

Error 'Unknown hardware' Appears After a Kernel Update

The following messages may be displayed during the start-up ALSA after the kernel update:

Unknown hardware "foo" "bar" ...
Hardware is initialized using a guess method
/usr/sbin/alsactl: set_control:nnnn:failed to obtain info for control #mm (No such file or directory)

or

Found hardware: "HDA-Intel" "VIA VT1705" "HDA:11064397,18490397,00100000" "0x1849" "0x0397"
Hardware is initialized using a generic method
/usr/sbin/alsactl: set_control:1328: failed to obtain info for control #1 (No such file or directory)
/usr/sbin/alsactl: set_control:1328: failed to obtain info for control #2 (No such file or directory)
/usr/sbin/alsactl: set_control:1328: failed to obtain info for control #25 (No such file or directory)
/usr/sbin/alsactl: set_control:1328: failed to obtain info for control #26 (No such file or directory)

Simply store ALSA mixer settings again (as root):

# alsactl -f /var/lib/alsa/asound.state store

It may be necessary configure ALSA again with alsamixer

HDA Analyzer

If the mappings to your audio pins(plugs) do not correspond but ALSA works fine, you could try HDA Analyzer -- a pyGTK2 GUI for HD-audio control can be found at the ALSA wiki. Try tweaking the Widget Control section of the PIN nodes, to make microphones IN and headphone jacks OUT. Referring to the Config Defaults heading is a good idea.

NOTE: the script is done by such way that it is incompatible with python3 (which is now shipped with ArchLinux) but tries to use it. The workaround is: open "run.py", find all occurences of "python" (2 occurences - one on the first line, and the second on the last line) and replace them all by "python2".

NOTE2: the script requires root acces, but running it via su/sudo is bogus. Run it via kdesu or gksu.

ALSA with SDL

If you get no sound via SDL and ALSA cannot be chosen from the application. Try setting the environmental variable SDL_AUDIODRIVER to alsa.

# export SDL_AUDIODRIVER=alsa

Low Sound Workaround

If you are facing low sound even after maxing out your speakers/headphones, you can give the softvol plugin a try. Add the following to /etc/asound.conf.

pcm.!default {
      type plug
      slave.pcm "softvol"
  }

pcm.softvol {
    type softvol
    slave {
        pcm "dmix"
    }
    control {
        name "Pre-Amp"
        card 0
    }
    min_dB -5.0
    max_dB 20.0
    resolution 6
}

After the changes are loaded successfully, you will see a Pre-Amp section in alsamixer. You can adjust the levels there.

Popping sound after resuming from suspension

You might hear a popping sound after resuming the computer from suspension. This can be fixed by editing /etc/pm/sleep.d/90alsa and removing the line that says aplay -d 1 /dev/zero

Example configurations

See Advanced Linux Sound Architecture/Example Configurations.

See also

• Advanced ALSA module configuration
• Unofficial ALSA Wiki
• HOWTO: Compile driver from svn