That can't really be allowed for side-to-side logic because it would be so very audible. It's another reason some gain-riding of the surround channel (separate from Constant Power operation) is permissible, in addition to the selective cancellation via matrix multiplier circuits a more 'discrete' effect can be achieved for hard-panned, surround only signals, by allowing a modest amount of gain riding power transfer. Shure Bros came across this in the initial design of their Stereosurround encoding process and the, to-this-day-unequaled, Acra-Vector Logic decoding for Dolby Stereo/Surround films and music the side-to-side logic action required to create a highly separated Center Front (from L/R Front) is always much more audible than even very heavy amounts of Logic required to keep L/R front fully separated from the mono surround since it's on the front to back axis. Thus, for any 'amount' of Logic action, SQ - by its virtue of its logic action being kept along the front/back axis - will always be less audible than any 'regular' matrix, due to its encoding/decoding specifications. For the left/right axis, in both the front and back channels, and even with a non-logic decoder (and no 10/40 or 10/20 blend), full separation is achieved at all times - and with 10% blend, it's reduced from 'infinity' (effectively the LP stylus or digital/tape source inherent levels) to 'only' 20db of separation, which is plenty for full stereo/quad localization, even when located directly next to the adjacent 'crosstalk bearing' speaker/channel. Humans are 20 times more sensitive to left/right amplitude (level) variations than to front/back variations or to phase changes: SQ reduced separation, and thus placed all logic action, only along the front/back axis. Sadly, the reduced Left/Right separation in both non-decoded stereo AND decoded (non-logic) Sansui QS playback is why the action of the Vario-Matrix is so audible to many listeners (and why Dolby dropped it from the experimental prototype theatrical Dolby Stereo units) unless expensive split-band techniques or vastly reduced levels of inter-channel separation are acceptable. I was up all night - absolutely no sleep, with stomach flu, so if this post makes no sense, I apologize.
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