[vorbis-dev] Re: Calling for 5.1 Mastering experience! (vorbis ambisonics and 5.1)

[ChristianHJW]

Gregory Maxwell wrote:
> I've been doing a fair amount of work with Vorbis support for Ambisonics,
> which seems to be going along nicely. It seems that there is signifant
> interest in coding 5.1 material with Vorbis esp as tarkin becomes more
> complete, so I've decided to take a break from pure ambisonic work to look
> into this.

Great to see there is work done on Vorbis 5.1 !!! Latest AAC encoders 
were slowly taking Vorbis position in the DVD backup scene, because AAC 
5.1 sounds quite nice at 200 - 240 kbps.

About your question :

 From an sound engineering perspective, a separate subwoofer channel is 
more or less useless, it could be muxed fine into the main Left and 
Right speakers, resulting in a 5.0 setup.

Never mux the signal into all channels, especially not the rear 
channels, as those speakers are normally

- not built to be able to generate low frequency stuff at all
- will act against the output of the main speakers, unless you inverse 
the phase by 180° , at least in a finite space = room. If you do 
inverse, to sum up the bass output from rear and front speakers, be sure 
there are a couple of setups where the 'rear' speakers are placed 
somewhere in the room where they found space, but not really in the 
rear, giving you problems again ;-) ...

About 5.1 vs. 5.0 again :

Only in very small rooms, where low frequencies can not even match the 
lambda/2 criterium from one wall to another ( again : finite space = 
room problem ) it could be possible that a subwoofer, placed in one 
corner of the room, could result in better low frequency performance.

Just my 2 cents :)

Christian

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