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Generalized Transaural Stereo and Applications
Transaural stereo is a signal-theoretic means for accurately generating precisely defined signals at the ears of a listener by using loudspeakers. As such, it is the basis for true loudspeaker-based three-dimensional sound and the benchmark against which all approximations are to be measured. The present work extends the prior art by applying standard methods of vector spaces so that the limitation on the number of loudspeakers and the number of listeners' ears at two each is removed. The implication of a certain set of solutions of the generalized transaural equations on loudspeaker and amplifier power requirements are examined and found to minimize the total power requirements. Generalized crosstalk cancelers, which in principle can accommodate any number of loudspeakers and any number of listeners, are introduced and several novel examples are worked out. The compact Lauridsen array, the only true stereo loudspeaker and the loudspeaker analog of the M-S microphone, is updated to transaural status. It offers intriguing applications, as do some variations on the original array. Basic transaural theory and analytical techniques, which are developed throughout, are then applied to the problem of layout reformatters in which the playback geometry of loudspeakers and/or listeners is different form that which was intended by the producer of the program material, but whereby it is desired to maintain fully accurate imaging in the new geometry. Another application that is addressed is the problem of having more discrete program channels than are available for transmission or storage. It is shown how to reconstruct the program exactly for a limited number of listeners. Despite the detail offered, the paper is highly conceptual in spirit. The authors share informally their experiences with designing and listening to various transaural systems and offer comments and guidance in areas in which future designers might encounter difficulty. Practical applications in several areas are suggested, including sound for high-definition television and digital video disk.
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