Roger Waters Amused to Death (and a number of albums from other artists) use the QSound mixing system. It essentially allows sound to be positioned anywhere within a half-sphere around the listener. Roger himself explains how it works in the following interview (from Rockline, Feb. 8, 1993):

    It divides any signal into a left and right component...(so it works with any stereo system), and it introduces minute delays at different frequency levels into left and right components to make your brain think that the sound is coming, not from in front of you -- from the two speakers -- but from in any one of a number of other positions around you. But you have to be sitting right between the two speakers, I mean exactly -- to within like an inch or an inch and a half [on] either side of the central perpendicular axis. And it is an amazing effect...