Create a new version of paste:

# dmix - plug:dmix supports 1-8 channels, and does use dmix!
# Whereas surround51 doesn't use dmix
# http://bbs.archlinux.org/viewtopic.php?pid=745946#p745946


# cat /proc/asound/card0/pcm0p/sub0/hw_params
# Output to hw:0,0 to keep at 44.1k rather than dmix's 48k
# 44.1k stops dmix from working, though.


# From https://bugs.launchpad.net/debian/+source/sdl-mixer1.2/+bug/66483
# Not needed.
#defaults.pcm.dmix_max_periods -1


#defaults.pcm.rate_converter "samplerate_best"

# See /usr/share/alsa/pcm/dmix.conf
#defaults.dmix.period_time 0
#defaults.dmix.periods 4
#defaults.pcm.surround51.device "0"


# From https://bugtrack.alsa-project.org/alsa-bug/view.php?id=1853
# Posted at http://bbs.archlinux.org/viewtopic.php?id=95582
# Is a dmix that actually works!
pcm.dmixed {
    @args [ CHANNELS ]
    @args.CHANNELS {
	type integer
	default 2
    }
    @args.CARD {
	type string
	default 0
    }
    @args.$DEV {
	type string
	default 0
    }
    @args.$SUBDEV {
	type string
	default 0
    }
    type asym
    playback.pcm {
	type dmix
	ipc_key 5678293
	ipc_perm 0660
	ipc_gid audio
	slave {
	    channels $CHANNELS
            pcm {
                type hw
                card $CARD
                device $DEV
                subdevice $SUBDEV
            }
            period_time {
                    @func refer
                    name {
                            @func concat
                            strings [
                                    "cards."
                                    {
                                            @func card_driver
                                            card $CARD
                                    }
                                    ".pcm.dmix.period_time"
                            ]
                    }
                    default -1
            }
                period_size {
                        @func refer
                        name {
                                @func concat
                                strings [
                                        "cards."
                                        {
                                                @func card_driver
                                                card $CARD
                                        }
                                        ".pcm.dmix.period_size"
                                ]
                        }
                        default 1024
	    }
                periods {
                        @func refer
                        name {
                                @func concat
                                strings [
                                        "cards."
                                        {
                                                @func card_driver
                                                card $CARD
                                        }
                                        ".pcm.dmix.periods"
                                ]
                        }
                        default 16
		}
	}
    }
    capture.pcm {
	type dsnoop
	ipc_key 5778293
	ipc_perm 0660
        slave {
            pcm {
                type hw
                card $CARD
                device $DEV
                subdevice $SUBDEV
            }
            period_size {
                    @func refer
                    name {
                            @func concat
                            strings [
                                    "cards."
                                    {
                                            @func card_driver
                                            card $CARD
                                    }
                                    ".pcm.dsnoop.period_size"
                            ]
                    }
                    default 1024
            }
            period_time {
                    @func refer
                    name {
                            @func concat
                            strings [
                                    "cards."
                                    {
                                            @func card_driver
                                            card $CARD
                                    }
                                    ".pcm.dsnoop.period_time"
                            ]
                    }
                    default -1
            }
            periods {
                    @func refer
                    name {
                            @func concat
                            strings [
                                    "cards."
                                    {
                                            @func card_driver
                                            card $CARD
                                    }
                                    ".pcm.dsnoop.periods"
                            ]
                    }
                    default 16
            }
	}
    }
}


# Playing
#pcm.!default {
#	type asym
#	playback.pcm "upmix_20to51_resample"
#}


# Check that e.g. Thief2 still works, if default is redefined.
#pcm.!default {
#	type plug
#	# Always output to all 6 channels, so the dmixer actually works if e.g. 6-channel is attempted to be started, while 2-channel is playing.
#	slave.pcm "dmixed:6"
#}

pcm.!surround20 {
	type plug
	slave.pcm "dmixed:6"
}

pcm.!surround40 {
	type plug
	slave.pcm "dmixed:6"
}

pcm.!surround51 {
	type plug
	slave.pcm "dmixed:6"
}


# If get error "Slave PCM not usable", then need to use plug:
# If get error "Cannot find rate converter", then install libsamplerate and alsa-plugins

# Lunar Linux:  lin ladspa-bs2b
# listplugins
# analyseplugin bs2b
pcm.bs2b {
	type ladspa
	path "/usr/lib/ladspa"
	plugins {
		0 {
			id 4221  # Bauer stereophonic-to-binaural (4221/bs2b)
			input {
				controls [ 700 6 ]
			}
		}
	}
	# http://bbs.archlinux.org/viewtopic.php?id=95582
	slave.pcm "plug:dmixed:6"
}


# speaker-test -D headphones -c 2 -t wav
# audacious uses less CPU when running bs2b as a listed plugin, probably because of samplerate_best
# Posted at http://bbs.archlinux.org/viewtopic.php?pid=626573#p626573
pcm.headphones {
	type rate
	slave {
		pcm "plug:bs2b"
		rate 48000
	}
	# Choices: samplerate_best samplerate_medium samplerate samplerate_order samplerate_linear
	converter "samplerate_best"

    hint {
        show on
        description "Headphones"
    }
}


pcm.ch51dup {
	slave.pcm "dmixed:6"
	slave.channels 6
	type route

	# Front and rear
	ttable.0.0 0.5
	ttable.1.1 0.5
	ttable.2.2 0.5
	ttable.3.3 0.5

	# Center and LFE
	ttable.4.4 1
	ttable.5.5 1

	# Front left/right to center
	ttable.0.4 0.5
	ttable.1.4 0.5

	# Front left/right to rear
	ttable.0.2 0.5
	ttable.1.3 0.5
}


# http://alsa.opensrc.org/SurroundSound
# http://alsa.opensrc.org/index.php/Low-pass_filter_for_subwoofer_channel_(HOWTO)
# Lunar:  lin ladspa tap-plugins swh-plugins cmt-plugins libsamplerate
# Fedora:  yum install ladspa ladspa-blop-plugins ladspa-caps-plugins ladspa-cmt-plugins ladspa-swh-plugins ladspa-tap-plugins libsamplerate
# Arch Linux:  pacman -S ladspa blop swh-plugins libsamplerate tap-plugins cmt
# For id 1672 - 4 Pole Low-Pass Filter with Resonance (FCRCIA) (1672/lp4pole_fcrcia_oa), install blop-plugins
# speaker-test -D upmix_20to51 -c 2 -t wav
# Debugging:  speaker-test -D plug:lowpass_21to21 -c 3 -t wav
# listplugins
# analyseplugin cmt
# http://plugin.org.uk/ladspa-swh/docs/ladspa-swh.html
# http://forums.gentoo.org/viewtopic-p-4528619.html#4528619
pcm.lowpass_21to21 {
	type ladspa
	slave.pcm upmix_21to51
	# Set the path to ladspa, to fix this error:
	# Playback open error: -2,No such file or directory
	path "/usr/lib/ladspa"
	channels 3
	plugins {
		0 {
			id 1098  # Identity (Audio) (1098/identity_audio)
			policy duplicate
			input.bindings.0 "Input";
			output.bindings.0 "Output";
		}

		#1 {
		#	id 1052  # High-pass filter
		#	policy none
		#	input.bindings.0 "Input";
		#	output.bindings.0 "Output";
		#	input {
		#		controls [ 300 ]
		#	}
		#}

		#2 {
		#	id 1052  # High-pass filter
		#	policy none
		#	input.bindings.1 "Input";
		#	output.bindings.1 "Output";
		#	input {
		#		controls [ 300 ]
		#	}
		#}

		#3 {
		#	id 1051  # Low-pass filter.
		#	policy none
		#	input.bindings.2 "Input";
		#	output.bindings.2 "Output";
		#	input {
		#		controls [ 300 ]
		#	}
		#}

		# From http://alsa.opensrc.org/index.php/Low-pass_filter_for_subwoofer_channel_(HOWTO)
		# Can be used instead of 1-3 above.
		1 {
			id 1672 # 4 Pole Low-Pass Filter with Resonance (FCRCIA) (1672/lp4pole_fcrcia_oa)
			policy none
			input.bindings.2 "Input";
			output.bindings.2 "Output";
			input {
				controls [ 300 2 ]
			}
		}
	}
}


# speaker-test -D upmix_20to51 -c 2 -t wav
# In audacious:  upmix_20to51
pcm.upmix_20to51 {
	type plug
	slave.pcm "lowpass_21to21"
	slave.channels 3
	ttable {
		0.0     1       # left channel
		1.1     1       # right channel
		0.2     0.5     # mix left and right ...
		1.2     0.5     # ... channel for subwoofer
	}

	# slave.rate 48000 makes CPU utilization 20% instead of 3%
	# Can't hear the difference with Audigy4 anyway.
	# slave.rate 44100 is 3%, so that proves audacious outputs 44100
	#slave.rate 48000
	#converter "samplerate"
	#slave.rate_converter "samplerate_best"
}


# In audacious:  upmix_20to51_resample
# aplay -D upmix_20to51_resample ~/alsa/samplerate-test/udial.wav
pcm.upmix_20to51_resample {
	type rate
	slave {
		pcm upmix_20to51
		#format S32_LE
		# Audigy4 upmixes to 48000 itself, and seems to use low-quality linear interpolation
		rate 48000
	}
	# Choices: samplerate_best samplerate_medium samplerate samplerate_order samplerate_linear
	# 8% CPU with samplerate_medium - good choice
	converter "samplerate_medium"
	#converter "samplerate_linear"
    hint {
        show on
        description "20to51"
    }
}

# Debugging:  speaker-test -D upmix_21to51 -c 3 -t wav
pcm.upmix_21to51 {
	type plug
	# For ice1724:
	#slave.pcm surround51-ice
	# For Audigy:
	slave.pcm "dmixed:6"
	# http://bbs.archlinux.org/viewtopic.php?pid=745946#p745946
	#slave.pcm dmixed:6
	# For P5K ADI:
	#slave.pcm surround51-adi
	# Trying to pipe through Pulse Audio, to stop the clicks between songs.
	# Can't get Pulse Audio to work like this.
	#slave.pcm pulse
	# Don't need to specify the number of channels.
	slave.channels 6
	ttable {
		0.0     1       # front left
		1.1     1       # front right
		0.2     1       # rear left
		1.3     1       # rear right

		# Front left/right to center.
		# Imbalanced because is to the left of the monitor!
		# Would normally be 0.5 each.
		0.4     0.5
		1.4     0.5

		# Subwoofer, more powerful to compensate for bass-removal from other speakers.
		2.5     2
    }
}


# Channels are wrong way around in doom! This fixes them.
# http://www.linuxforen.de/forums/archive/index.php/t-206470.html
# http://forums.seriouszone.com/showthread.php?t=49869&page=10
# http://forums.gentoo.org/viewtopic-p-4173170.html#4173170
# For Audigy 4
# Weird, doom3 has crappy sound if I add an alsa rate converter.
# Posted at http://ubuntuforums.org/showthread.php?t=1304228
pcm.doom-surround51 {
	slave.pcm "dmixed:6"
	slave.channels 6
	type route
	ttable.0.0 1
	ttable.1.1 1
	ttable.2.4 1
	ttable.3.5 1
	ttable.4.2 1
	ttable.5.3 1
}


pcm.doom3-8930g {
	type plug
	slave.pcm {
		type dmix
		ipc_key 1093  # Must be unique
		ipc_key_add_uid false
		ipc_perm 0660
		slave {
			pcm "hw:0,0"
			rate 44100
			channels 2
			period_time 0
			period_size 1024
			buffer_time 0
			# Doom 3 wants buffer_size 8192
			# In ~/.doom3/base/autoexec.cfg
			# And ~/.quake4/q4base/autoexec.cfg
			# seta s_alsa_pcm "doom3-8930g"
			buffer_size 8192
		}
	}
}