Enabling nForce4 optical SPDIF output

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Background

Many users with Nvidia4 based motherboards have problems enabling the digital audio output (optical and/or coax) from their motherboard in Linux. The default values set by the alsa driver do not enable the digital output, and it is not possible to enable it using the alsamixer.

A solution was found by changing the asound.state file directly.

Short howto:

  1. Close mythfrontend if it is running.
  2. Save the asound.state file below to ~/asound.state
  3. Enter the command alsactl -f ~/asound.state restore See "Troubleshooting" below if this command returns any errors.
  4. Once the alsactl command can be run without error, start mythfrontend.
  5. In mythfrontend go to Utilities/Setup -> Setup -> General and for Audio output device put ALSA:digital. However, if the next step doesn't work, you may need to enter ALSA:default instead.
  6. Test both surround sound output and stereo output. Try watching a standard definition or analogue TV channel (for a stereo test) and a DVD with Dolby and/or DTS surround sound (for a surround sound test).


Once everything is working satisfactory, you will want to ensure that these changes are preserved after reboot.

  1. Locate your distributions existing asound.state file. It is usually located at /etc/asound.state or /var/lib/alsa/asound.state The command alsactl --help helped me find the default location in Ubuntu. Refer to your distributions documentation for further guidance.
  2. Change into the directory of your distributions asound.state file cd /etc or cd /var/lib/alsa (or per your distribution).
  3. Create a backup copy of your distributions existing asound.state cp asound.state asound.state.orig
  4. Move the file that you created above, to replace your distributions mv ~/asound.state asound.state
  5. Enter the command alsactl restore if there are no errors then you should be done.
  6. If there are errors stating that 'no state is present for XXX' where XXX is any device other than CK804, locate the devices state in your original asound.state.orig file and copy into the new asound.state

Troubleshooting

Due to differences in the ALSA driver and the support circuits you might experience error messages of the following kind:

alsactl: set_control:894: warning: name mismatch (Mic Boost (+20dB)/Mic Boost (+20dB) Capture Switch) for control #17
alsactl: set_control:896: warning: index mismatch (0/0) for control #17
alsactl: set_control:898: failed to obtain info for control #17 (Operation not permitted)

This means that on your hardware, the name of control #17 is not "Mic Boost (+20dB) Capture Switch" but instead "Mic Boost (+20dB)". To fix this problem, edit the asound.state file and change the name of control to the correct name.

Control #30 may also give this error. Change its name in asound.state from "Mic Select Capture Switch" to "Mic Select".

You may also receive an error of the form:

alsactl: set_control:1273: failed to obtain info for control #17 (No such file or directory)

This is less helpful, as you will need to find the correct name for the control using a program such as alsamixer, which should hopefully be quite simple to figure out, since the name of each control is shown in the upper left corner.

If the name is not clear from alsamixer then you will want to try to locate the name of the control from your distributions existing asound.state file. The 2nd half of the howto above has instructions for locating your distributions asound.state file. Once you find it, read though it to find the correct name for the control.

The last error you may receive is 

No state is present for card CX8811

This refers to another sound card or sound hardware on a TV tuner card in the system. If you're not using that card for your sound output (and if you are, then this page is of no use to you!), then this message can be safely ignored.

asound.state File

Save the following file as ~/asound.state

~/asound.state 

state.CK804 {
	control.1 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'Master Playback Switch'
		value true
	}
	control.2 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 2
		comment.range '0 - 31'
		iface MIXER
		name 'Master Playback Volume'
		value.0 22
		value.1 22
	}
	control.3 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'Center Playback Switch'
		value false
	}
	control.4 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 1
		comment.range '0 - 31'
		iface MIXER
		name 'Center Playback Volume'
		value 31
	}
	control.5 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'LFE Playback Switch'
		value true
	}
	control.6 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 1
		comment.range '0 - 31'
		iface MIXER
		name 'LFE Playback Volume'
		value 13
	}
	control.7 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 2
		iface MIXER
		name 'Surround Playback Switch'
		value.0 false
		value.1 false
	}
	control.8 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 2
		comment.range '0 - 31'
		iface MIXER
		name 'Surround Playback Volume'
		value.0 0
		value.1 0
	}
	control.9 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'Master Mono Playback Switch'
		value false
	}
	control.10 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 1
		comment.range '0 - 31'
		iface MIXER
		name 'Master Mono Playback Volume'
		value 0
	}
	control.11 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'PC Speaker Playback Switch'
		value false
	}
	control.12 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 1
		comment.range '0 - 15'
		iface MIXER
		name 'PC Speaker Playback Volume'
		value 0
	}
	control.13 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'Phone Playback Switch'
		value false
	}
	control.14 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 1
		comment.range '0 - 31'
		iface MIXER
		name 'Phone Playback Volume'
		value 0
	}
	control.15 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'Mic Playback Switch'
		value false
	}
	control.16 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 1
		comment.range '0 - 31'
		iface MIXER
		name 'Mic Playback Volume'
		value 0
	}
	control.17 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'Mic Boost (+20dB) Capture Switch'
		value false
	}
	control.18 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'Line Playback Switch'
		value false
	}
	control.19 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 2
		comment.range '0 - 31'
		iface MIXER
		name 'Line Playback Volume'
		value.0 0
		value.1 0
	}
	control.20 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'CD Playback Switch'
		value false
	}
	control.21 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 2
		comment.range '0 - 31'
		iface MIXER
		name 'CD Playback Volume'
		value.0 0
		value.1 0
	}
	control.22 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'Aux Playback Switch'
		value false
	}
	control.23 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 2
		comment.range '0 - 31'
		iface MIXER
		name 'Aux Playback Volume'
		value.0 0
		value.1 0
	}
	control.24 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'PCM Playback Switch'
		value true
	}
	control.25 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 2
		comment.range '0 - 31'
		iface MIXER
		name 'PCM Playback Volume'
		value.0 22
		value.1 22
	}
	control.26 {
		comment.access 'read write'
		comment.type ENUMERATED
		comment.count 2
		comment.item.0 Mic
		comment.item.1 CD
		comment.item.2 Video
		comment.item.3 Aux
		comment.item.4 Line
		comment.item.5 Mix
		comment.item.6 'Mix Mono'
		comment.item.7 Phone
		iface MIXER
		name 'Capture Source'
		value.0 Mic
		value.1 Mic
	}
	control.27 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'Capture Switch'
		value true
	}
	control.28 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 2
		comment.range '0 - 15'
		iface MIXER
		name 'Capture Volume'
		value.0 0
		value.1 0
	}
	control.29 {
		comment.access 'read write'
		comment.type ENUMERATED
		comment.count 1
		comment.item.0 Mix
		comment.item.1 Mic
		iface MIXER
		name 'Mono Output Select'
		value Mix
	}
	control.30 {
		comment.access 'read write'
		comment.type ENUMERATED
		comment.count 1
		comment.item.0 Mic1
		comment.item.1 Mic2
		iface MIXER
		name 'Mic Select Capture Switch'
		value Mic1
	}
	control.31 {
		comment.access read
		comment.type IEC958
		comment.count 1
		iface MIXER
		name 'IEC958 Playback Con Mask'
		value '0fff000f00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000'
	}
	control.32 {
		comment.access read
		comment.type IEC958
		comment.count 1
		iface MIXER
		name 'IEC958 Playback Pro Mask'
		value cf00000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
	}
	control.33 {
		comment.access 'read write'
		comment.type IEC958
		comment.count 1
		iface MIXER
		name 'IEC958 Playback Default'
		value '0082000200000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000'
	}
	control.34 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'IEC958 Playback Switch'
		value true
	}
	control.35 {
		comment.access 'read write'
		comment.type INTEGER
		comment.count 1
		comment.range '0 - 3'
		iface MIXER
		name 'IEC958 Playback AC97-SPSA'
		value 0
	}
	control.36 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'Duplicate Front'
		value false
	}
	control.37 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'Mic Front Input Switch'
		value false
	}
	control.38 {
		comment.access 'read write'
		comment.type ENUMERATED
		comment.count 1
		comment.item.0 Shared
		comment.item.1 Independent
		iface MIXER
		name 'Surround Jack Mode'
		value Shared
	}
	control.39 {
		comment.access 'read write'
		comment.type ENUMERATED
		comment.count 1
		comment.item.0 '2ch'
		comment.item.1 '4ch'
		comment.item.2 '6ch'
		iface MIXER
		name 'Channel Mode'
		value '2ch'
	}
	control.40 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'IEC958 Capture Switch'
		value false
	}
	control.41 {
		comment.access 'read write'
		comment.type ENUMERATED
		comment.count 1
		comment.item.0 PCM
		comment.item.1 'Analog In'
		comment.item.2 'IEC958 In'
		iface MIXER
		name 'IEC958 Playback Source'
		value PCM
	}
	control.42 {
		comment.access 'read write'
		comment.type BOOLEAN
		comment.count 1
		iface MIXER
		name 'External Amplifier'
		value true
	}
}
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