Advanced Linux Sound Architecture/Configuration examples

The following should serve as a guide for more advanced ALSA setups. The configuration takes place in /etc/asound.conf as mentioned in the main article. None of the following configurations are guaranteed to work.

Note: Most things discussed here are much easier to accomplish using alsa plugins like upmix which are explained in the main article.

Upmixing of stereo sources to 7.1 using dmix while saturated sources do not get upmixed

# 2008-11-15
#
# This .asoundrc will allow the following:
#
# - upmix stereo files to 7.1 speakers.
# - playback real 7.1 sounds, on 7.1 speakers,
# - allow the playback of both stereo (upmixed) and surround(7.1) sources at the same time.
# - use the 6th and 7th channel (side speakers) as a separate soundcard, i.e. for headphones
#   (This is called the "alternate" output throughout the file, device names prefixed with 'a')
# - play mono sources in stereo (like skype & ekiga) on the alterate output
#
# Make sure you have "8 Channels" and NOT "6 Channels" selected in alsamixer!
#
# Please try the following commands, to make sure everything is working as it should.
#
# To test stereo upmix :      speaker-test -c2 -Ddefault -twav
# To test surround(5.1):      speaker-test -c6 -Dplug:dmix6 -twav
# To test surround(7.1):      speaker-test -c6 -Dplug:dmix8 -twav
# To test alternative output: speaker-test -c2 -Daduplex -twav
# To test mono upmix:         speaker-test -c1 -Dmonoduplex -twav
#
#
# It may not work out of the box for all cards. If it doesnt work for you, read the comments throughout the file.
# The basis of this file was written by wishie of #alsa, and then modified with info from various sources by 
# squisher. Svenstaro modified it for 7.1 output support.

#Define the soundcard to use
pcm.snd_card {
    type hw
    card 0
    device 0
}

# 8 channel dmix - output whatever audio, to all 8 speakers
pcm.dmix8 {
    type dmix
    ipc_key 1024
    ipc_key_add_uid false
    ipc_perm 0660
    slave {
        pcm "snd_card"
        rate 48000
        channels 8
        period_time 0
        period_size 1024
        buffer_time 0
        buffer_size 5120
    }

# Some cards, like the "nforce" variants require the following to be uncommented. 
# It routes the audio to the correct speakers.
#    bindings {
#        0 0
#        1 1
#        2 4
#        3 5
#        4 2
#        5 3
#        6 6
#        7 7
#    }
}

# upmixing - duplicate stereo data to all 8 channels
pcm.ch71dup {
    type route
    slave.pcm dmix8
    slave.channels 8
    ttable.0.0 1
    ttable.1.1 1
    ttable.0.2 1
    ttable.1.3 1
    ttable.0.4 0.5
    ttable.1.4 0.5
    ttable.0.5 0.5
    ttable.1.5 0.5
    ttable.0.6 1
    ttable.1.7 1
}

# this creates a six channel soundcard
# and outputs to the eight channel one
# i.e. for usage in mplayer I had to define in ~/.mplayer/config:
#   ao=alsa:device=dmix6
#   channels=6
pcm.dmix6 {
    type route
    slave.pcm dmix8
    slave.channels 8
    ttable.0.0 1
    ttable.1.1 1
    ttable.2.2 1
    ttable.3.3 1
    ttable.4.4 1
    ttable.5.5 1
    ttable.6.6 1
    ttable.7.7 1
}

# share the microphone, i.e. because virtualbox grabs it by default
pcm.microphone {
    type dsnoop
    ipc_key 1027
    slave {
        pcm "snd_card"
    }
}

# rate conversion, needed i.e. for wine
pcm.2chplug {
    type plug
    slave.pcm "ch71dup"
}
pcm.a2chplug {
    type plug
    slave.pcm "dmix8"
}

# routes the channel for the alternative
# 2 channel output, which becomes the 7th and 8th channel 
# on the real soundcard
#pcm.alt2ch {
#    type route
#    slave.pcm "a2chplug"
#    slave.channels 8
#    ttable.0.6    1
#    ttable.1.7    1
#}

# skype and ekiga are only mono, so route left channel to the right channel
# note: this gets routed to the alternative 2 channels
pcm.mono_playback {
    type route
    slave.pcm "a2chplug"
    slave.channels 8
    # Send Skype channel 0 to the L and R speakers at full volume
    #ttable.0.6    1
    #ttable.0.7    1
}

# 'full-duplex' device for use with aoss
pcm.duplex {
    type asym
    playback.pcm "2chplug"
    capture.pcm "microphone"
}

#pcm.aduplex {
#    type asym
#    playback.pcm "alt2ch"
#    capture.pcm "microphone"
#}

pcm.monoduplex {
    type asym
    playback.pcm "mono_playback"
    capture.pcm "microphone"
}

# for aoss
pcm.dsp0 "duplex"
ctl.mixer0 "duplex"

# softvol manages volume in alsa
# i.e. wine likes this
pcm.mainvol {
    type softvol
    slave.pcm "duplex"
    control {
        name "2ch-Upmix Master"
        card 0
    }
}

#pcm.!default "mainvol"

# set the default device according to the environment
# variable ALSA_DEFAULT_PCM and default to mainvol
pcm.!default {
    @func refer
    name { @func concat 
           strings [ "pcm."
                     { @func getenv
                       vars [ ALSA_DEFAULT_PCM ]
                       default "mainvol"
                     }
           ]
         }
}

# uncomment the following if you want to be able to control
# the mixer device through environment variables as well
#ctl.!default {
#    @func refer
#    name { @func concat 
#           strings [ "ctl."
#                     { @func getenv
#                       vars [ ALSA_DEFAULT_CTL
#                              ALSA_DEFAULT_PCM
#                       ]
#                       default "duplex"
#                     }
#           ]
#         }
#}

Surround51 incl. upmix stereo & dmix, swap L/R, bad speaker position in room

Bad practice but works fine for almost everything without additional per-program/file customization:

pcm.!default {
    type route
## forwards to the mixer pcm defined below
    slave.pcm dmix51
    slave.channels 6

## "Native Channels" stereo, swap left/right
    ttable.0.1 1
    ttable.1.0 1
## original normal left/right commented out
#    ttable.0.0 1
#    ttable.1.1 1

## route "native surround" so it still works but weaken signal (+ RL/RF swap) 
## because my rear speakers are more like random than really behind me
    ttable.2.3 0.7
    ttable.3.2 0.7
    ttable.4.4 0.7
    ttable.5.5 0.7

## stereo => quad speaker "upmix" for "rear" speakers + swap L/R
    ttable.0.3 1
    ttable.1.2 1

## stereo L+R => join to Center & Subwoofer 50%/50%
    ttable.0.4 0.5
    ttable.1.4 0.5
    ttable.0.5 0.5
    ttable.1.5 0.5
## to test: "$ speaker-test -c6 -twav" and: "$ speaker-test -c2 -twav"
}

pcm.dmix51 {
	type dmix
	ipc_key 1024
# let multiple users share
	ipc_key_add_uid false 
# IPC permissions (octal, default 0600)
# I think changing this fixed something - but I'm not sure what.
	ipc_perm 0660 # 
	slave {
## this is specific to my hda_intel. Often hd:0 is just allready it; To find: $ aplay -L 
		pcm surround51 
# this rate makes my soundcard crackle
#		rate 44100
# this rate stops flash in firefox from playing audio, but I do not need that
       rate 48000
       channels 6
## Any other values in the 4 lines below seem to make my soundcard crackle, too
       period_time 0
       period_size 1024
       buffer_time 0
       buffer_size 4096
	}
}

Loopback interface with dmix external interface

Used to control which output goes to external, loopback, or both. Others have reported working setups without specifying format

# Use this to output to external
pcm.dmixerout {
 type dmix
 ipc_key 1024
 ipc_key_add_uid false
 slave {
  pcm "hw:CARDNAME,0"
  channels 2
  period_time 0
  period_size 1024
  buffer_size 4096
  rate 44100
 }
 bindings {
  0 0
  1 1
 }
}

# Use this to output to loopback
pcm.dmixerloop {
 type dmix
 ipc_key 2048
 ipc_key_add_uid false
 slave {
  pcm "hw:Loopback,0,0"
  channels 2
  period_time 0
  period_size 1024
  buffer_size 4096
  # If format is absent ALSA gives me slave PCM not usable, but it works w/o it for others
  format S32_LE
  rate 44100
 }
 bindings {
  0 0
  1 1
 }
}

# Sends to the two dmix interfaces
pcm.quad {
 type multi
 # Necessary to have both slaves be dmix; both as hw doesn't give errors, but wouldn't 
 slaves.a.pcm "dmixerout"
 slaves.a.channels 2
 slaves.b.pcm "dmixerloop"
 slaves.b.channels 2
 bindings {
  0 { slave a; channel 0; }
  1 { slave a; channel 1; }
  2 { slave b; channel 0; }
  3 { slave b; channel 1; }
 }
}

# Duplicates to quad, use this to output to loopback & external
pcm.stereo2quad {
 type route
 slave.pcm "quad"
 # ttable.A.B G
 # where A - input channel
 #       B - output channel
 #       G - volume gain (1.0 = original)
 ttable.0.0 1
 ttable.1.1 1
 ttable.0.2 1
 ttable.1.3 1
}

# Listens to loopback
# trying to play to stereo2quad when something is already listening gives me slave PCM not usable
# but listening when something is already playing on stereo2quad works
# and so does starting to listen, then playing to dmixerloop
pcm.loopin {
 type dsnoop
 ipc_key 1111
 ipc_key_add_uid false
 slave.pcm "hw:Loopback,1"
}

pcm.!default {
 type asym
 playback.pcm "plug:stereo2quad"
 capture.pcm "plug:loopin"
}