Quadraphony: Developments in matrix H decoding

The basic form of decoder is a complex-coefficient linear matrix, but this has an inherent lack of separation between the output signals. Logic enhancement techniques are discussed, which seek to improve interchannel separations for the principal sound-source, at the expense of secondary sources. As an interim measure, a modified commercial logic-enhanced (Variomatrix) decoder was studied, which led to the development of a purpose-built logic-enhanced decoder for Matrix H. The latter combines the virtues of both linear Matrix H decoding, and the variable-matrix logic enhancement technique. All the decoders described are capable of providing a good surround-sound reproduction. In particular, a purpose-built Matrix H logic-enhanced decoder has been shown to exhibit a performance very close to a discrete 4-channel system; the failings normally associated with logic-enhanced decoders are almost inaudible.