======ALSA-only audio on Linux======
this is a guide on how to setup ALSA to be enjoyable by itself without an audio server.

I will be showing changes to ///etc/asound.conf// as to effect all users (including daemons such as MPD). you can also use //~/.asoundrc// for setup specific to your user.

=====devices=====
multiple commands can list available audio cards and devices.

**alsactl** can be used:
<code bash>
$ alsactl info 1
#
# Sound card
#
- card: 1                    # card number.
  id: sofhdadsp
  name: sof-hda-dsp
  longname: 
  driver_name: sof-hda-dsp
  mixer_name: Realtek ALC233
  components: 
  controls_count: 54
  pcm:
    - stream: PLAYBACK
      devices:
        - device: 1          # device number.
          id: HDA Analog (*) # name.
          name: 
          subdevices:
            - subdevice: 0
              name: subdevice #0
...
</code>
by default //alsactl info// will show card 0. you most likely have multiple cards.

**aplay** will also list sound cards and devices.
<code bash>
$ aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: HDMI [HDA ATI HDMI], device 0: HDMI 0 [HDMI 0]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
...
card 1: sofhdadsp [sof-hda-dsp], device 1: HDA Analog (*) []
  Subdevices: 1/1
  Subdevice #0: subdevice #0
...
</code>

card 1 and device 1 will be used for this guide. in most places, this is specified with **"hw:1,1"**. the first number is the card and the second is the device.

=====mixing=====
[[https://www.alsa-project.org/wiki/Asoundrc#dmix|dmix]] is a software mixer for audio output. it will allow multiple programs to simultaneously play sound at the same time.

in //asound.conf//, the following configuration could be used to create a software mixer that can be accessed by multiple users.
<file bash /etc/asound.conf>
pcm.mixer {
  type dmix
  ipc_key 1024
  ipc_key_add_uid false  # remove these two lines to only allow
  ipc_perm 0666          #  one user to use the mixer at a time.
  
  slave {
    pcm "hw:1,1"         # hardware output device to use.
  }
}

pcm.!default plug:mixer  # set the default device to the mixer.
</file>

=====S/PDIF multichannel=====
the **a52** alsa plugin can be used to output Dolby Digital 5.1 (or lower) multichannel audio through S/PDIF.

you must have the plugin installed. look in your distribution's repositories for a package similar to "alsa-plugins". it may be in a separate package such as "alsa-plugins-a52", as on Alpine Linux.

here is an example configuration:
<file bash /etc/asound.conf>
pcm.surround {
        type a52
        slavepcm "hw:1,1"

        channels 6
        bitrate 1000
        rate 48000
        format S16_LE
}
</file>


=====equalization=====
[[https://github.com/bassdr/alsaequal|alsaequal]] is a 10-band software equalizer in the form of an ALSA plugin.

each user has their own persistent settings, stored in //~/.alsaequal.bin//. if, for example, you are running MPD as its own mpd user, you must either copy or link the //alsaequal.bin// file to its home directory, or manually configure it seperately.

the following configuration builds on the previous section on dmix. an asoundrc using solely alsaequal can be very simple.
<file bash /etc/asound.conf>
pcm.dmix_stereo {
        type dmix
        ipc_key 1024
        ipc_key_add_uid false
        ipc_perm 0666

        slave {
                pcm "hw:1,1"

                period_time 0
                period_size 1024
                buffer_size 4096
                rate 48000
        }
        bindings {                     # channel configuration (stereo, quad, 5.1, ...).
                0 0
                1 1
        }
}
pcm.plug_eq_stereo {
        type equal
        slave.pcm "plug:dmix_stereo"
}
pcm.eq_stereo {                       # this plug is needed to make the alsaequal output suitable for use by most applications.
        type plug
        slave.pcm "plug_eq_stereo"
}

ctl.eq_stereo {                       # this ctl is what allows adjustment in alsamixer (or similar utilities).
        type equal
}

pcm.!default eq_stereo
</file>
with this configuration, the equalizer can be changed with ctl **eq_stereo**:
<code bash>
alsamixer -D eq_stereo
</code>

====multichannel====
here is an example of using alsaequal with **a52**.
<file bash /etc/asound.conf>
...

pcm.surround {
        type a52
        slavepcm "hw:1,1"

        channels 6
        bitrate 1000
        rate 48000
        format S16_LE
}
pcm.plug_eq_surround {
        type equal
        channels 6                         # changes channel configuration to 5.1.
        controls ".alsaequal.surround.bin" # sets the control information file to at ~/.alsaequal.surround.bin. this must be changed if there are to be multiple alsaequals of differing channel configurations.
        slave.pcm "plug:surround"
}
pcm.eq_surround {
        type plug
        slave.pcm "plug_eq_surround"
}

ctl.eq_surround {
        type equal
        channels 6
        controls ".alsaequal.surround.bin"
}

...
</file>
the surround equalizer can be changed with ctl **eq_surround** using this configuration.

{{tag>audio alsa linux}}