Originally Posted by MagnumX
Out of phase is still out of phase. "Uncorrelated" really just means out of phase.
Yes, but I hope you agree that opposite polarity is a special case of "out-of-phase". IOW, all uncorrelated signals are out of phase, but not all out-of-phase signals are uncorrelated (zero correlation). They can be negatively correlated.
The degree to which a sound is out of phase can be easily measured (e.g. on an oscilloscope). This is used to create "stereo" rear output in DPLII. DPLI soundtracks typically went 180 degrees out of phase if they wanted to use the rear speakers.
Same for PLII encoding, BTW.
I think you'd find very little content if you extracted out of phase (i.e. Surround output) using one DPLII decoder and its surround outputs from an extracted extra channel (i.e. Center output is say front wides and you want to use the surround outputs for even more speakers). That is because the out of phase content for surround is the in phase content for the mains. They've already been extracted so there's not much left there.
I may not be following, but if you are saying that it would be fruitless to try to further decode the surrounds of a 2-ch source decoded with PLII, that is correct. The 7.1 mode of PLIIx is completely different for 2-ch sources, and does not use a secondary logic decoder as is done for 5.1 sources.
Now with discrete surround that's not necessarily the case as they could put full phase sounds in just those speakers, but this isn't likely to be common.
The point of processing the surrounds is not to extract the out-of-phase content, but to ignore that and derive intermediate speaker feeds between the source channels for signals with correlation from 0 to 1. Can derive one new output as in a "Surround EX" style 6.1 layout, or derive two as in a PLIIx style 7.1 layout. Two is better than one when it comes to rear surround speakers for various well known reasons.
But where would you put those speakers? The other side if the room (i.e. Behind each set of front wides?). That's the other set of front wides so shouldn't it already be on that side of the room? Without decoding, it'd be forward/backward of the speakers in question (behind front wall and further back into room beyond the side surrounds. Again, there's already speakers there (rear surrounds). In other words, it's mostly moot, IMO.
If there are sufficient speakers in place to produce the degree of localization desired, no need to add further decoding and intermediate speakers. The only motive for all of this is to produce real sound images in place of phantom images to better solidify localization for various listening positions. Not to move sounds to different locations.
The best use is center extraction between pairs.
That's indeed the best if you want one new output between a given pair. If you want two outputs between the pair, you need a 4-ch decoder.
Deadwood II Theater
(Previous Deadwood Theater HTOM
Anthem AVM 60 7.4.4; Classé SSP-800 PLIIx 7.4; MiniDSP OpenDRC-AN
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Adam Audio S3V/S3H LCR, KEF Ci200QS 4 srrnd, Tannoy Di6 DC 4 hts, Hsu ULS-15 4 subs
JVC RS520; Stewart Cima Neve screen 125" diag 2.35:1, MLP at 115"