Reviewing in perspective the -codes- available for matrix quadraphony, the following criteria were adopted which, while not exhaustive, are considered to be essential. 1) The front-channel separation in the stereophonic mode should be total and any -panned- front signals should be in phase. (This ensures stereophonic compatibility.) 2) The four corner channels sould be transmitted in the monophonic mode at equal levels. (This is a requirement for monophonic compatibility.) 3) The matrix decoder should be capable of unambiguous positioning of the encoded signals without change of relative signal power over a 360° compass. (This ensures high fidelity quadraphonic reproduction even with a simple matrix decoder.) The following codes are identified with various matrix proposals: square resistive matrix; New Orleans matrix; New Orleans with 45° relative rotation; New Orleans with 90° relative rotation; regular matrix, SQ matrix, and SQ matrix with position encoding. It is shown that only the latter two meet the aforementioned criteria. The principles of blend, logic, and variblend enhancement are described and a hierarchy of decoders is projected from the simplest (matrix with fixed blend) to the most comprehensive (full-logic with wave-matching and signal-adaptive variable blend). A -paramatrix- logic which in the future would embrace all optimum alternatives is envisioned.
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