[mythtv-users] 7+1 audio with alsa, xine and 5+1 DVDs

Franco mythtv at email.it
Sun Jun 12 22:42:29 UTC 2005

Hello Mike,

> Check out the comment in /usr/share/alsa/pcm/surround71.conf
> (although I'm pretty sure the last two are 6 and 7 instead of 7 and 8)

Ok, found it;

> Check out /usr/share/alsa/cards/<your card name>.conf to see if your card uses a 
> different mapping (i.e look at the <card name>.pcm.surround71.0 and see 
> if there's a ttable

Ok, it's   /usr/share/alsa/cards/Audigy2.conf
and the interested section is Audigy2.pcm.surround71.0
Luckily, there was no ttable ;-)

> (this is completely untested, so no guarantees):
> pcm.ch51to71 {
>   type route
>   slave.pcm surround71
>   slave.channels 8
>   ttable.0.0 1
>   ....
> Make sure you set xine to use this ALSA device for 5.1-ch output and 
> then use 5.1-channel output.

I put it in my .asoundrc, configured xine and... it works! :-)
It seems you were also right with channel numbering (6 and 7, not 7 and 8 )

> You could also try sending both the front and rear channels to the side 
> ttable.0.6 0.25
> ttable.2.6 0.75
> ttable.1.7 0.25
> ttable.3.7 0.75
> but I would expect that to be worse 

Yes, it is. My friends were there when I was testing
so I have multiple opinions on that... they all had
no hesitation in stating the first solution was sounding
better. The effects are more clear in the first case,
transitions are sharper. In the second case when there 
is some sound moving in the room, it's blended, blurred,
how to say, not so clear and sharply posizioned in space.

> You may like it better at 0.5/0.5, but I was afraid that 
> would completely wash out the position information

No, maybe 0.1/0.9 but my friends didn't even want to try... :-)

> It's also possible to copy only the rear channels at 75% volume instead 
> of 100% (i.e. replace the 1 with 0.75).

I want to try this next...  however you first solution just sounded
_much better_ than before.   Louder volume, better effects, even 
dialogues were understandable.

Think, the speakers were carefully positioned in the room 
in a 7.1 arrangement, and this arrangement does not correspond
to the position information recorded in a 5.1 movie.

> Please let me know how (if :) this works for you and what you think of 
> the different configs compared to the untouched 5.1 output and the 
> hardware-upmixed output you describe below.

See above... also, seemed me even better than the hardware upmix
(I'm referring to the amplifier upmix and not the soundcard CMSS,
not available under Linux) but we didn't do direct test on this.

I'll do next time... :-)

Thank you again,

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