ALSA/troubleshooting

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ALSA troubleshooting

For in-depth information about a program's usage of ALSA, such as its PID (owner_pid) and sample rate (rate), use the /proc interface. This can be done by substituting the relevant card/device details into the following command. Note that the /proc interface only lists physical devices, not virtual devices[1].

user $cat /proc/asound/card2/pcm0p/sub0/*
access: RW_INTERLEAVED
format: S16_LE
subformat: STD
channels: 2
rate: 44100 (44100/1)
period_size: 5513
buffer_size: 22050
card: 2
device: 0
subdevice: 0
stream: PLAYBACK
id: USB Audio
name: USB Audio
subname: subdevice #0
class: 0
subclass: 0
subdevices_count: 1
subdevices_avail: 0
state: RUNNING
owner_pid   : 934
trigger_time: 86393.193574796
tstamp      : 86540.250594985
delay       : 17714
avail       : 4602
avail_max   : 7379
-----
hw_ptr      : 6485052
appl_ptr    : 6502500
tstamp_mode: NONE
period_step: 1
avail_min: 5513
start_threshold: 2147483647
stop_threshold: 22050
silence_threshold: 0
silence_size: 0
boundary: 6206523236469964800

No sound

If there's no sound, output channels may be muted. Unmute the channels, either by using the GUI environment's mixer, or by using alsamixer (from the media-audio/alsa-utils package), selecting the appropriate channels and pressing the M key to mute or unmute:

user $alsamixer

Custom ALSA config results in no sound in browsers

Try explicitly specifying defaults in the configuration:

FILE ~/.asoundrc
defaults.pcm.card <number of default sound card>
defaults.ctl.card <default sound card>

Note that, since Firefox 52 (released in 2017), support for direct output to ALSA has been dropped, and PulseAudio has been made a hard requirement. To address this, enable Firefox's pulseaudio flag and install apulse, which provides Pulse emulation for ALSA

Sound card only available for one application

Sometimes one app essentially takes over all sound devices, e.g. for performance reasons.

To force the use of dmix instead of direct audio output (which is what most things, such as Wine, use by default), when the device is card 1 device 7:

FILE ~/.asoundrc
pcm.dmixed {
    type asym
    playback.pcm {
        type dmix
        ipc_key 5678293
        ipc_perm 0660
        ipc_gid audio
 
        slave {
            channels 2
            pcm {
                format S16_LE # S32_LE
                rate 48000 # Can also be 44100
                type hw
                card 1 # Specify card number as appropriate
                device 7 # Specify device number as appropriate
                subdevice 0
            }
 
            period_size 1024
            buffer_size 8192
        }
 
        bindings {
            0 0
            1 1
# Uncomment below if using 6 channel
#           2 2
#           3 3
#           4 4
#           5 5
        }
    }
    capture.pcm "hw:0"
}
 
pcm.!default {
    type plug
    slave.pcm "dmixed"
}

Use of ~/.asoundrc is immediate: as long as use of a specific device is not being forced by any applications, applications will either begin to produce audio output immediately, or will require a restart. One of the best tests is to open a browser, go to YouTube, open a terminal, and use an audio or video player to try to play an audio or video file: success is indicated by an absence of errors (e.g. "Device or resource busy").

Missing dialogue/sound with 4.0 speakers

If using a 4.0 sound card (like an old SB Live), or 4.0 speakers in general, the dialogue in some games or movies might be very quiet or even missing. This is because most applications and movies support only either 2.0 (stereo) or 5.1 output. In order to achieve surround sound, the 5.1 audio track is used, but two channels are discarded: the center channel (which usually carries dialogue), and the subwoofer channel.

This issue can be circumvented by creating a virtual device which downmixes 5.1 to 4.0, mixing the center and subwoofer channels with other audio channels.

FILE ~/.asoundrc
pcm.downmix {
    type route
 
    slave {
        # The sound card output to be used
        pcm surround40
        # Real number of output channels
        channels 4
    }
 
# ttable.A.B G
# where A - input channel
#       B - output channel
#       G - volume gain (1.0 = original)
 
# Copy channels 0-3
    ttable.0.0 1
    ttable.1.1 1
    ttable.2.2 1
    ttable.3.3 1
 
# Mix channel 4 (center) into front speakers, and a bit (0.3) into rear ones
    ttable.4.0 1.0
    ttable.4.1 1.0
    ttable.4.2 0.3
    ttable.4.3 0.3
 
# Mix channel 5 (subwoofer) mostly (0.6) into rear speakers, and a bit (0.3) into front ones
    ttable.5.0 0.3
    ttable.5.1 0.3
    ttable.5.2 0.6
    ttable.5.3 0.6
}
 
ctl.downmix {
    type hw
    card 0
}

HDMI output from aplay has incorrect speaker channels

If MPlayer or VLC correctly plays a file in a 5.1 or 7.1 configuration over HDMI, but aplay doesn't, this might be caused by the snd_hda_intel HDMI audio module/driver, which is used by vendors other than Intel (e.g. Nvidia). Additionally, aplay might refuse to play the file if its format is 24-bit PCM 2.0/5.1 WAV.

To address these issues with minimal alterations to the PCM streams, remap the speaker channels. The following configuration is for both 5.1 and 7.1 audio. (If audio from a 7.1 stream should not be omitted, further map/copy the two extra channels to the 5.1 channels.) Additionally, as most HDMI-to Stereo-receiver connections only stream 16- and 32- bit formats, skipping 24-bit, the configuration up-mixes any PCM stream using the pcm.myHDMI profile to 32 bits.

FILE /etc/asound.conf
pcm.myHDMI {
    type plug
    slave {
        pcm "hw:1,7"
        format S32_LE
        channels 6
    }
    ttable {
        0.0= 1
        1.1= 1
        2.4= 1
        3.5= 1
        4.2= 1
        5.3= 1
        6.6= 1
        7.7= 1
    }
}

Weak center channel on PCM 5.1 live music

If a multi-channel soundtrack or piece of music has an apparently weak center channel, and the sound track is a live recording, it might be possible to map the center channel to the rear channels, e.g. when using mplayer:

user $mplayer -ao alsa:device=hw=1.7 Music/MyAlbum/PCM51-24bit/01.MyMusic.wav -channels 6 -format s32le -af channels=6:6:0:0:1:1:4:2:4:3:4:4:5:5

The above incantation of mplayer specifies:

  • an HDMI device of hw:1.7;
  • the PCM 5.1 audio file;
  • the number of channels;
  • the format (not needed if the receiver can natively handle 24 bit; receivers that can only natively handle 16- or 32-bit audio need to be upmixed); and
  • the mapping.

The mapping specifies:

  • a 6 channel audio stream, with 6 mappings immediately following, then to copy:
  • the left front channel to left speaker;
  • the right channel to right speaker;
  • the center channel to left rear speaker;
  • the center channel to right rear speaker;
  • the center channel to center speaker; and
  • the subwoofer channel to the subwoofer speaker.

Note that the rear channels on live recordings usually contain only the audience screaming, with very little music.

For further details, refer to the mplayer(1) man page.

Laptops with HDMI audio output

Some laptops with HDMI audio output will map HDMI as /proc/asound/card0, making it the default output device for applications. To change the device order, refer to the "Kernel modules" section.

Headset jack not working

Sometimes, to get a headset jack working, additional model information needs to be passed to the audio driver. For example, in case of a Dell Latitude E7470 laptop with snd-hda-intel driver, the following needs to be added to /etc/modprobe.d/alsa.conf:

FILE /etc/modprobe.d/alsa.conf
options snd-hda-intel model=headset-mic

More information can be found in this section of the Linux kernel documentation.

udev/alsactl errors on boot

Due to partitioning, encryption, or having a split /usr system, these errors may appear on boot:

root #journalctl -b | grep alsa
 
(udev-worker)[2594]: controlC2: Process '/usr/sbin/alsactl restore 2' failed with exit code 2.
 
(udev-worker)[2611]: controlC0: Process '/usr/sbin/alsactl restore 0' failed with exit code 2.
 
(udev-worker)[2579]: controlC1: Process '/usr/sbin/alsactl restore 1' failed with exit code 2.

To fix the issue, add TEST=="@sbindir@/alsactl" to /lib/udev/rules.d/90-alsa-restore.rules:

FILE /lib/udev/rules.d/90-alsa-restore.rules
TEST!="/etc/alsa/state-daemon.conf", TEST=="@sbindir@/alsactl", RUN+="/usr/sbin/alsactl restore $attr{device/number}"
TEST=="/etc/alsa/state-daemon.conf", TEST=="@sbindir@/alsactl", RUN+="/usr/sbin/alsactl nrestore $attr{device/number}"

For further details and discussion, refer to this discussion on alsa-devel and this discussion on bugs.debian.org.

No sound after rebooting following a system update

If, after a system update followed by a reboot, sound is not working, resulting in e.g. speaker-test(1) producing an error like: 

 ALSA lib /var/tmp/portage/media-libs/alsa-lib-1.2.14/work/alsa-lib-1.2.14/src/pcm/pcm_dmix.c:1000:(snd_pcm_dmix_open) unable to open slave
 Playback open error: -2,No such file or directory

and alsaplayer(1) producing an error like: 

 /usr/lib64/alsaplayer/output/libalsa_out.so failed to load
 NOTE: THIS IS THE NULL PLUGIN.      YOU WILL NOT HEAR SOUND!!

It might be that a stale /var/lib/alsa/asound.state file is present (e.g. due to the format of that file changing between kernel versions). Remove that file and reboot.

References

  1. ↑ ALSA project - the C library reference : Control interface : General overview
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