[mythtv-users] how to tell if 5.1 audio channels mapped correctly?

Frans Grotepass fmgrotepass at yahoo.co.uk
Tue Nov 9 08:17:14 UTC 2010


On Sunday 07 November 2010 18:37:24 Jan Schneider wrote:
> Zitat von Jean-Yves Avenard <jyavenard at gmail.com>:
> > Hi
> > 
> > On 6 November 2010 05:57, Dan Christensen <jdc at uwo.ca> wrote:
> >> Well, there's good news and bad news.  The good news is that I now see
> >> the pattern.  Whenever I get digital passthrough to work with a piece
> >> of software (myth AC3/DTS, mplayer DTS and xine DTS), the playback is
> >> correct.  But whenever I don't use digital passthrough, the playback
> >> is wrong, including with mythtv!  For example, with
> >> 
> >>  http://www.avenard.org/files/media/videotest/audiotest/idch_AviaSurroun
> >> dTest-DTS.mkv
> >> 
> >> played back in myth without digital passthrough, the center and left
> >> surround channels are swapped, and it sounds like the LFE and right
> >> surround channels are swapped too (but I don't have a subwoofer, so
> >> it's harder to tell).
> >> 
> >> So now it looks like I have a systematic problem with channel mappings.
> >> 
> >> Could it be because the version of alsa I'm running is older than yours?
> >> I'm running Debian lenny with these alsa versions
> > 
> > If the channel order is consistent when using LPCM ; it could very
> > well be your amplifier ... Otherwise you can remap it easily with an
> > alsa configuration.
> > 
> > The way I test LPCM on my box is through the analog output ; and I can
> > tell you it's correct.
> > 
> > This PC is still running Ubuntu 9.10. Will probably upgrade to 10.04
> > LTS at some stage : but as they say ; if it ain't broken.. And this is
> > my main frontend.
> 
> This thread got me curious, so I've run your test videos on my FE. The
> MB is connected to the amplifier through S/PDIF, and the amp's
> internal speaker test assures that all speakers are working and
> connected correctly.
> If I run the 5.1 test videos though, I don't get any sound from the
> surround (rear) speakers. MythTV is configured to use the digital alsa
> port, DD and DTS passthrough, upsampling of stereo.
> I don't have a /etc/asound.conf file.
> Any hints?
> 
> Jan.
Incredibly, I've also had similar problems since upgrading my set-up a while 
ago. Most of the stuff I watch is stereo, so the exact point when it went wrong 
is not clear. I use Gentoo. As is already mentioned, it could be broken in the 
kernel, ALSA or mythtv.

I have the problem on AAC 5.1 on both my HDMI (using the ati hdmi driver) for 
the HD4200 chip and the realtek onboard sound using s/pdif on my HTPC. For 
this reason I am struggling to lay it on a driver quirk as is suggested. My 
bets are on ALSA or mythtv. Will have to check the versions tonight and post 
what is known not to work.

 


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