[mythtv] [mythtv-commits] Ticket #1104: multichannel audio support

[Paul Catchpole]

Mark Spieth wrote:
> play with params.dimension in FreeSurround constructor.
> 0..100 moves the soundfield backwards. 0 is default.
> perhaps a number > 0 for music mode is warranted. Ill let others decide as 
> my 5.1 setup has the rears at the side as the wires arent long enough to go 
> far.
> center_width is similar. 0 is all centre energy is in centre. 100 is all in 
> l/r and none in centre (I think)
> I chose 50 for music mode and 0 for movie mode. Opinions on music mode 
> choice?
>
>   
I'll have a play with the settings. I've since stopped being a donkey 
and remembered that I can control the rear, front and lfe levels 
separately from the mixer - just not the overall master!
> 6ch is only swapped s that they come out the correct channel. no real upmix 
> is done though it uses the library to do this.
> upmix is only done on 2ch audio. 4ch audio is not currently handled. unsure 
> as to the best alternative is for this but Ive never seen a 4ch audio track. 
> Ill handle it when someone complains. :-)
> use a SD 2ch soundtrack. or any 2ch AVI. they sound great compared to 
> passive mode.
>
> The major difference in passive mode between the previous incarnation and 
> this one is that stretch is done in 6ch instead of 2ch so may be slightly 
> worse performance wise for those with gutless 6ch out systems (sorry adam)
>
>   
Cool, no worries. It doesn't seem to have added much of a performance 
overhead here, but this frontend is okay CPU-wise.
> I also see you still use liba52. any reason why?
> obviously works though so it is a good test. Ive only rtied with internal 
> ac3 dec.
>   
Erm, no good reason! I seem to remember that when I first started 
playing with getting multi-channel decoding to work, I couldn't get the 
then-current SVN trunk to compile with the internal ac3, so used liba52 
instead! I'll switch back and give it another go.

I've one problem with it, now we've been using it for a few hours - I'm 
getting a crackle from the centre speaker which is intermittent although 
not random. It varies from a sharp click, to a buzz and is in sync with 
the sound on the channel. It has the following characteristics:

* Master output volume level changes the volume of the click, but 
doesn't alter its proportion to the other sounds.
* Changing the centre channel mixer level makes the clicking quieter, 
but doesn't alter its proportion to the other sounds on the centre channel.

I'm getting the feeling that it is directly proportional to the quantity 
of very low frequency sounds in the source. It was particularly bad 
earlier on 'Creature Comforts' and is extremely bad, now and again, 
watching [well, my better half is] the X-Factor. Commercials almost 
always don't cause it. It does happen on the news channels.

I know that's perhaps not a lot to go on, but if you've any ideas I'd 
appreciate it.

In the mean time, I'll try and get a recording which causes it, and 
capture a sample.

Cheers,

PC

PS: I've checked it is still okay with the plain SVN build - I've not 
blown up the centre speaker!