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

[Paul Catchpole]

Paul Catchpole wrote:
> 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!
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>   
In addition to what I've said about the crackle being caused by 
low-frequency source peaks, it also caused very definitely by applause - 
even if the source volume of that applause is quite low.

Hope that might help!

PC

PS: My other half, Kate, would like to make it clear that I put the 
X-Factor on, not her. She does appreciate your hard work, however. :-)