高级Linux音频架构/配置示例

以下内容应作为更高级 ALSA 设置的指南。配置在主文章中提到的 /etc/asound.conf 中进行。以下配置均不保证有效。

注意： 这里讨论的大多数事情都可以使用 alsa 插件（如 upmix）更容易地完成，这在主文章中已解释。

将立体声源上混为 7.1 声道，同时饱和音源不进行上混

# 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 包括立体声上混 & dmix，交换左右声道，房间中扬声器位置不佳

不良实践，但对于几乎所有内容都适用，无需额外的程序/文件自定义

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
	}
}

使用 dmix 外部接口的回环接口

用于控制哪个输出到外部、回环或两者。其他人报告了无需指定格式即可工作的设置 [1]

# 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"
}