[flac-dev] Define 6.1 and 7.1 channel mappings

[Stephen F. Booth]

On Sunday, September 23, 2012 at 2:04 PM, Ralph Giles wrote:
> On Fri Sep 21 16:31:21 2012, Stephen F. Booth wrote:
> 
> > 6.1: L R C LFE Ls Rs Cs (MPEG 6.1 A layout)
I should have been clearer with the labels I was using:

L = Left
R = Right
C = Center
LFE = Low frequency effects
Ls = Left surround
Rs = Right surround
Cs = Center surround
Rls = Rear left surround
Rrs = Rear right surround
 
> 
> Having read a bit more:
> 
> This matches the WAV (or USB) order if you map Ls (Left Surround?) to
> Back Left and Rs (Right surround) to Back Right, instead of mapping them
> to Side Left and Side Right as I do.
> 
> Practically, there's not much difference in what you call these for 6.1.
> If you only have 7 speakers, the signals go to the surround speakers
> regardless, and if you have 8, the matrix should send the surround
> signals to both side and back speakers.
> 
> 

 I think that's true.  I was using the nomenclature that Apple uses for Core Audio as that is what I'm most familiar with.
> 
> I chose the 'Side' label over 'Back' based on the suggested ideal
> placement diagrammes at sites like crutchfield.com (http://crutchfield.com) and dolby.com (http://dolby.com), and
> dolby's reference to the 'back surround' speakers in 7.1 as being the
> extra ones, not the side speakers.
> 
> So the question is, how to choose between mapping surround to "side" and
> mapping it to "left". Can you elaborate on "what Apple has done" and why
> we should chose the other way?
> 
> 

Apple doesn't actually force any channel orderings, so I may have been slightly unclear when I said that is what they have done.  However, they provide a long list of predefined channel layouts provided by various groups- MPEG, ITU, DVD, etc.  Apple lists the following ITU defined layouts:

1.0: C
2.0: L R
2.1: L R Cs
2.2. L R Ls Rs
3.0: L R C
3.1: L R C Cs
3.2: L R C Ls Rs
3.2.1: L R C LFE Ls Rs
3.4.1: L R C LFE Ls Rs Rls Rrs

Annoyingly, I can't find the ITU mapping for 6.1 although I think my suggestion from earlier is still reasonable.  ITU 775-3 specifies some channel orderings (http://www.itu.int/dms_pubrec/itu-r/rec/bs/R-REC-BS.775-3-201208-I!!PDF-E.pdf) but I couldn't find anything for 6.1 or 7.1.  It may be in a different document I didn't find.
> > 7.1: L R C LFE Ls Rs Rls Rrs (MPEG 7.1 B layout)
> 
> 
> Here I just disagree. This is the same set of labels as in my proposal,
> but the order does *not* match WAV order, assuming Ls->left side and
> Rls->back left.
> 
> 

You're correct in the meanings of the channel labels, but I actually mistyped and the layout should be called MPEG 7.1 C.  I tried to pick the layout I thought was most in line with the other FLAC layouts.

Stephen
> 
> -r 

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