Enabling nForce4 optical SPDIF output

Background

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

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

Short howto:

1. save the asound.state file below as "/etc/asound.state"
2. Enter the command "alsactl restore"
   

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)" but instead "Mic Boost (+20dB) Capture Switch".

To fix this problem, edit the /etc/asound.state file and change the name of control to the correct name.

3. Fix any problems in the asound.state file as described above.

4. Test your setup by playing an audio file while using the optical output. The optical output should now be able to output regular stereo and surround depending on your audio source.

/etc/asound.state File

Save the following file as /etc/asound.state Template:Box File

MythTV Setup

Now, once the file is saved start/restart mythfrontend.

Go to Utilities/Setup -> Setup -> General and for Audio output device put ALSA:digital.