[mythtv-users] AC3 Passthrough issues

Matt skd5aner at gmail.com
Mon Mar 13 02:24:10 UTC 2006


On 3/12/06, Michael T. Dean <mtdean at thirdcontact.com> wrote:
> On 03/12/2006 08:33 PM, Matt wrote:
> >   I've been searching around, and I can't quite find someone having
> > the same issue I'm having.  I've got alsa with SPDIF passthrough.
> > It's been working great for analog shows,
>
> Note that you cannot have "passthrough" with analog.  Passthrough is
> used to pass an AC-3/DTS stream directly through Myth to the receiver.
> For analog TV, Myth outputs PCM data, instead, because there is no
> AC-3/DTS stream to pass through.

Right, I understand.  I guess I meant that it worked via spdif optical
out, not necessarily "digital sound" passthrough for the receiver to
decode.

>
> >  and I just installed my
> > digital cards this weekend.  I recorded an HD broadcast today, Nascar,
> > and when I started to play it, all I heard was the cars.  I didn't
> > hear announcers, sound effects... nothing besides "VROOOOM".  So... I
> > figured... interesting.
> >
> > I went into the menu and saw that the first audio channel said AC3
> > 5.1.  So, I figured "This is only playing a few of the channels".
> > However, it happens on all the HD stations.  I've tried many of the
> > suggestions I found for passthrough, but none of them worked.  I'd
> > either get no sound, or the same sound.
> >
> > The interesting thing is, that when I played analog, my receiver would
> > show "PCM 48K" and play just fine.  When I played the digital, nothing
> > showed up on the receiver screen and it just played the sounds.  When
> > commercials came up, you could hear a little more, but you could tell
> > much was missing.
> >
> > Any clues?
> >
> > Here's my .asoundrc file:
> >
> > ## Uncomment the following to use mixed digital by default
> >   slave.pcm "dmix-digital"
> >
>
> Don't use dmix.  Change your default to "digital" (uncomment the
> "digital-hw" line and comment the "dmix-digital" line).
>

Alright...  I did that... funny thing happened:
1) watched the show, heard voices, and there was seperation of
channels.  However, the receiver did not say it was decoding
anything.. YAY?  No...
2) Closed the show... re-opened... no sound
3) Closed it again... waited a few seconds, reopened... same thing as
before... only the sound of the cars, no announcers.  I also have
westwing.  I could hear the dramtic music, but no talking.  It sounds
like I'm getting L/R but no center or rear.

Also... I have myth set to ALSA:digital and the mixer set to "digital"
and the drop down next to the set to PCM.

I can still verify that analog shows get sent to the receiver as PCM.

What now?

Thanks!
Matt


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