[mythtv-users] MythMusic and only 2 audio channels - no surround?

David myth at dgreaves.com
Thu Mar 31 16:32:46 UTC 2005


Peter Valdemar Morch wrote:

> David myth-at-dgreaves.com |Lists| wrote:
>
>> Check to see if alsamixer has got a '3D' or 'duplicate front' switch set
>>
>> I doubt it's mythmusic - it'll (probably) just send the stereo signal 
>> to the pcm channel.
>>
>> Also, another option, on my setup it all goes from the pc (via spdif) 
>> to an external hi-fi surround processor and I have to turn the 
>> pro-logic setting off on the processor to prevent it from trying to 
>> decode the stereo into 'surround sound'.
>>
>> what hardware setup do you have (ie soundcard -> amplifiers)
>
>
> I'm using a Sound Blaster Audigy2 and Alsa on a Creative Labs 
> Gigaworks 750 7.1 speaker system.

OK.

>
> I've tried configuring Xine and mplayer to just send out 2.0 stereo 
> (an mp3 music file), and yes, the sound comes out of all speakers, not 
> just the front ones. Now I don't know where the upmixing is done.
>
> If I set the ALSA 'Center' and 'Surround' settings to 0 with:
> amixer set Center 0
> amixer set Surround 0
> , the sound only comes from the two front speakers. But then that is 
> true regardless of whether the source is 2.0 or 5.1. :-(
>
> So it seems 2.0 stereo is upmixed to 5.1 in or before ALSA.. But where?
>
> Isn't this a good diagram:
>
> MPlayer \    --------   ---------------   --------------   --------
>          +---| Alsa |---| snd-emu10k1 |---| Audigy2 HW |---|GW 750|
> Xine    /    --------   ---------------   --------------   --------
>
> Since I can adjust the center and rear speaker volumes in alsamixer, 
> and it then works/applies for both xine and mplayer, then my guess is 
> that the upmixing is taking place in ALSA, right? Or is that done in 
> both MPlayer and Xine? If its taking place in ALSA, how do I disable it?
>
> <minor_question>
> Where do I find any documentation for what the different controls 
> actually precisely mean? Such as 'LFE', 'PCM' etc? Anyway, the '3D 
> Control - Switch' is off. And what all the alsa.conf settings mean?
> </minor_question>

no easy reference that I know of...
LFE - Low Frequency Effects (subwoofer rumbles)
PCM - pulse coded modulation - erm, digital (CD/wav) audio format

> amixer output:

all looks OK.

try: http://www.alsa-project.org/~james/speaker-test/

David


David



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