[mythtv-users] AC3 Passthrough on SB Audigy 4

[Henry A Harper III]

> 	I apologize if this has been asked a million times
> before, but I've gone through all the wiki's and howto's I can
> find and I just can't get the AC3 passthrough to work with MythTV
> on my setup. Either I end up with no audio or I end up with
> static. I can get 2-channel stereo audio to work fine on the
> SPDIF optical output with SD & HD channels, but no 5.1 audio on
> the HD channels. Video works fine.
> 	First, here's my system info:
>
> Pentium D @ 3.2 GHz w/2GB RAM
> pcHDTV HD-5500 tuner card
> Sound Blaster Audigy 4 (non-pro version) w/digital I/O module
> Kenwood surround sound receiver (connected via optical cable)
 <snip>
> 	What does this mean? The ALSA documentation appears to be
> developer-oriented, not user-oriented (at least beyond basic
> setup procedures), so I have no idea what's going on here.
> 	The pass-through works fine running Windows XP Pro on the
> same box - I tested it by playing a DVD in Windows Media Player
> and the 5.1 audio was routed to my receiver without a problem.
> The receiver is working fine with my stand-alone DVD player and
> my HD cable box, so there's nothing wrong with the receiver or
> any of my speakers. There's apparently nothing wrong with the
> sound hardware in the PC, either.
> 	I really don't know what I'm missing here, so if somebody
> can offer assistance, I'd appreciate it. Maybe someone with a
> similar setup could please send me a copy of their .asoundrc file
> and/or a screenshot of their "Audio" setup screen in
> mythfrontend?

I had an Audigy 2 ZS (that I got, amusingly in hindsight, because it "should
just work") that uses the same ALSA driver (emu10k1) as the Audigy 4. In the
same boat as you, after too much fiddling to try to get AC3 passthrough to
work, I finally found a passage on the alsa-project.org driver page to the
effect that AC3 passthrough for the emu10k1 module was *not "yet"
implemented*. I can't find that exact wording right now but the wiki page
http://bugtrack.alsa-project.org/main/index.php/Matrix:Module-emu10k1 does
not currently list "Digital AC3 out" under the "things that should work"
section.

==>> LESSON LEARNED (for me anyway): carefully read ALSA wiki *before*
purchasing sound devices for GNU/Linux use!

My solution was to ditch the Audigy 2 ZS and throw in a Turtle Beach Riviera
($29!!!) which has "known to work with AC3" reports. Indeed, it does "just
work" with the "Default" passthrough device. My motherboard also has onboard
audio with SPDIF header pins but I didn't really want to mess with
finding/making a connector. Gave the Audigy to a friend, w/suitable warning.

Now if only my local ABC, CBS, and NBC stations would actually *use* AC3 for
5.1...KTVB has the equipment but seems to downmix to front 3 channels except
for the Olympics, other two are PCM only so far.