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

Michael T. Dean mtdean at thirdcontact.com
Mon Jun 13 03:40:39 UTC 2005

Franco wrote:

>>(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 )
Wow.  That doesn't happen often.  :)

>>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... :-)
Sounds interesting...

>>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... :-)
Now you have me wondering how Creative implemented the amp's hardware 
upmix...  I really assumed they'd be computing the values, but maybe 
they assumed that since you have the sound card it wasn't worth the 
extra expense to put the electronics in the amp, too.

Thanks for reporting back.  Since I couldn't test it myself, I was 
really interested in hearing how it works (and how close I was :).  I 
have to admit that I'm surprised it's better than the 5.1 untouched--I 
thought the speakers that were used for 5.1 were close enough to their 
"5.1 positions," but it sounds like the difference is big enough to 
degrade the quality.

Now I'm wondering what would happen if you used the rear channels to all 
4 back speakers but reduced the volumes on them (to maybe 0.5 or 0.75)...

Anyway, enjoy.


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