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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