With a 7.1 true hd stream, the dolby digital core obviously has the rears folded into the surrounds, if you down mix 5.1 or 7.1 into plain 2.0 pcm (without dolby surround encoding), all channels are folded into the fronts, but with the appropriate phase angles. Run a stereo down mix of a 5.1 track through Dolby Pro logic II and 90% of the original surround track is restored with startling accuracy in my experience. In current 5.1 and 7.1 mixes, sounds originating from overhead, such as an airplane takeoff or helicopter, have the sound with the appropriate phase angles for overhead sound amorphously mixed into the surrounds, since a proper setup places the surround slightly above the listener, the sort of has the illusion of being overhead. Run this through Pro logic IIz and the sound actually does come from overhead now.
I'm curious if a similar scenario will happen with atmos. Will the height channels be blended into the surrounds and then be able to be approximately extracted via PLIIz. I'm guess it won't simply because the height channels aren't really channels at all, but objects placed into a 3 dimensional sound space.
Thoughts?
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