[mythtv-users] 5.1 wrong speaker problem

Jean-Yves Avenard jyavenard at gmail.com
Wed Jan 26 14:59:40 UTC 2011


Hi

On 26 January 2011 07:37, Ken Bass <kbass at kenbass.com> wrote:

> When I playback a 5.1 program, the center channel seems to be going to the
> REAR left. How can this happen?

The ION / 9400M nvidia chipset has an incorrect channel ordering. It
is set to SMPTE ordering only and not alsa ordering (or more exactly,
it can not be reconfigured).

There are no easy way around it but remap the channels using a custom
alsa configuration.

This topic has been discussed earlier.

the other way around it is to not use multi-channels PCM but force
using AC3 or DTS only.
In the advanced audio config, check the StereoPCM box.

Problem solved.

> Shouldn't the sound be sent unmolested directly to my audio receiver and it
> would decodes it there?
Not if using multichannels LPCM. Only when using AC3, DTS or other
encoding technique

> These recordings were make using a HD-PVR ( w/ SPDIF )
>
> I do have the boxes checked that says my system suppports dolby and dts.

You must have configured mythtv in such a way that audio processing is
required (e.g. resampling, upmixing, downmixing, software volume
etc..). As the audio is decoded and multichannels audio is supported,
it doesn't get re-encoded it and send it as LPCM.

This issue only occurs with ION1 or 9400M based machine.

Jean-Yves


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