No switching between analog and digital audio output on the nForce3

The audio output on my MythTV system is connected to a reasonably nice stereo, and it feeds the stereo both analog and digital audio, depending on whether you tell it to use ALSA:mixed-analog or ALSA:mixed digital as the playback audio device. I frequently switch between the two. HD broadcasts use digital sound, as do DVDs, but due to a quirk in the wiring, I need to use analog sound if I want to route the sound to my television and use TV volume controls.

I’m not the first person to have this problem, so I was hopeful when I found an article about switching the playback source with a remote control button in the MythTV wiki. In that article, there’s a script that uses the amixer command to switch the “IEC958 Playback Source”

#!/bin/sh

# Get current setting of PCM/analog switch
AUDIO=`amixer get ‘IEC958 Playback Source’ | grep ‘Item0:’ | cut -d\’ -f 2`

if [ “${AUDIO}” == “PCM” ]; then
# Route analog signal to S/PDIF
amixer set ‘IEC958 Playback Source’,0 ‘Analog’
# Could also be: sudo /sbin/alsactl -f /home/mythtv/asound.analog2spdif restore 0
else
# Route PCM signal to S/PDIF
amixer set ‘IEC958 Playback Source’,0 ‘PCM’
# Could also be: sudo /sbin/alsactl -f /home/mythtv/asound.pcm2spdif restore 0
fi

Excited, I opened a command line to see if I had support for selecting the audio source, but found that my nForce3 doesn’t support it:

myth ~ # amixer | grep IEC958
Simple mixer control ‘IEC958’,0
Simple mixer control ‘IEC958 Playback AC97-SPSA’,0

Nuts! I’ve filed this mentally under the reasons why I want to do a hardware re-spin on my Myth sytem. Although all of the parts were reasonable selections at the time, I would like to replace the noisy 60 mm fans in the Silverstone case (and maybe get a few more drive bays while I’m at it), and get a bit more processing power for transcoding.

One Response to “No switching between analog and digital audio output on the nForce3”

  1. […] Southbridge. I’m not real picky on this chip, but there is one feature I’d like. It’s apparently possible to watch sports without listening to inane announcers by muting the center channel audio in a 5.1 broadcast. My receiver has the tools for doing this, but there may be some support required in the audio chipset. […]

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