GB1396352A - Apparatus for reproducing quadraphonic sound - Google Patents

Abstract

1396352 Quadraphonic systems CBS Inc 23 June 1972 [23 June 1971] 29584/72 Heading H4 A decoding matrix, Fig. 2A, for quadraphonic signals coded by the arrangement described in Specification 1,387,874, producing L T and R T signals as shown at 38 and 40; derives four signals 90, 92, 94, 96, containing respectively predominant L # , Lb, Rb and R # in a conventional fashion using phase shift networks 46 to 52 and adders 70, 72, as described in Specifications 1,387,874 and 1,379,771. The signals L<SP>1</SP> # and R1 # are each combined with a minor proportion of the other signal in adders 98, 100, to produce the signals L<SP>11</SP> # and R<SP>11</SP> # for reproduction at the front corners of the listening area. Similarly the signals L<SP>1</SP>b and R<SP>1</SP> b are each combined with minor proportions of the other in adders 102 and 104 to produce the signal L<SP>11</SP> b and R11 b for reproduction in the rear corners of the listening area. Gain controlled amplifiers 74-80, are provided to feed the reproducers and are controlled by the logic circuit, Fig. 2b. The major portion of the logic circuit is similar to that described in Specification 1,387,873, and comprises a wave matching logic, producing at the output of difference circuit 172 a signal indicating predominance of front left or right signals by one polarity of output and predominance of rear left or right signals by the other polarity of output. In addition adders 190, 192 and difference circuit 206, which are similar to the "front-back" logic circuit of Specification 1,387,874, provide discrimination between a front centre signal and a rear centre signal to provide an appropriate output signal at 208. Signals at 208 above a predetermined threshold defined by diodes 210 and 212, are applied to adder 176, together with the output of the other logic circuit from 174, to provide gain switching potentials on lines 179 and 181 which differentially vary the gains of the amplifiers feeding the front speakers relative that of the amplifiers feeding the rear speakers.