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I'm guessing you all probably know why I need to create one of the above - to trick a Pro Logic Surround decoder.

Problem is, I know what a 90 - and 180 - deg phase shift looks like on a pure sinewave, but how to I achieve 90 degrees phase shift on "real world" material - a clip of ducks quacking or a 1890s locomotive roaring by? There is no simple wave - ducks, trains, and of course music - are anything but simple!