[mythtv] [mythtv-commits] Ticket #1104: multichannelaudio support

Paul Catchpole paul at paulcatchpole.co.uk
Thu Jan 10 18:45:10 UTC 2008


Ed Wildgoose wrote:
>> It works fine with the audio device for the frontend changed to a 
>> 2-channel one. It's only when using the real 6-channel device and hence 
>> the upmixer where the clipping occurs.
>>   
>>     
> #Often you have multiple volume controls for multichannel versus two 
> channel - perhaps the multichannel mixer is too loud and causing the 
> clipping?
>
> Ed
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>   
The 2-channel device used for testing is a simple ALSA upmixer with an 
additional soft-volume added on top. I set the relative mixer levels a 
long while ago and they've not changed since. I don't have a master on 
this card, hence the softvol. I don't change the levels to test the 5.1 
direct output, just move to another device which is the surround51 with 
a softvol on top.

For the previous testing I did of patch-38 [I think], where I had 
clipping problems, I tried reducing mixer levels to no avail - the 
'clipped' output just happily scaled with the rest of the sound.

I think Mark is probably correct in thinking it's a mathematical issue 
with the new upmixer code, which seems to use lots of floating-point 
maths...

PC


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