[mythtv-users] Funny problem with alsa and AC3 passthrough / rate conversion

[Meatwad]

David Maher wrote:
> Hi 
> I am using ALSA rate conversion for my analogue tuner with spdif output
> on my intel8x0 based onboard sound card. I'm using the .asoundrc from
> here http://www.mythtv.info/moin.cgi/DigitalSoundHowTo
> 
> Everthing was working fine using ALSA:mixed-digital, but lately, if I
> enable AC3 passthrough in the mythfrontend, my amp outputs a horrible
> buzzing sound when it gets a dolby digital signal from myth.
> 
> Ok, you say, something's wrong with the amp? No I don't believe so. 
> If I change my audio out string to ALSA:plug:iec958, the AC3 passthrough
> works fine, the digital tv tuner's audio is fine, but the analogue tv
> tuner's 32khz audio stream is choppy and speeds up dramatically. I guess
> this would be the expected behaviour. 
> 
> If I go back to ALSA:mixed-digital and turn off AC3 pass through,
> everthing works fine, as long as I don't want to listen to dolby
> surround. 
> Anyway, if anyone has any suggestions, or perhaps a different .asoundrc,
> that I should try I would be very grateful

In Kmix, got to the Switches tab. Enabling "IEC958 Output" solved this 
problem for me.

Here's my .asoundrc:

	pcm.cmipci {
	type hw
	card 0
	}
	
	ctl.cmipci {
	type hw
	card 0
	}

You would need to replace the two instances of pcm.cmipci with the 
appropriate one for your intel chipset -- pcm.intel8x0 I believe.

In Setup -> General -> Audio -> Audio Output Device, I use 
"ALSA:default" and have Enable AC3 Passthrough enabled.

Oddly, the alsactl store command in combination with Jarod's script 
doesn't always reset the Kmix settings after a reboot and I need to 
adjust Kmix again.

HTH