GB1384610A - Apparatus for reproducing quadraphonic sound - Google Patents

Abstract

1384610 Quadraphonic systems SONYCORP 15 June 1972 [21 June 1971] 28111/72 Heading H4R A decoder for a matrixed quadraphonic sound reproduction system has all pass phase shifting networks in the dematrixing circuit. Each phase-shift network includes a phase splitter, the outputs of which are used to derive gain logic switching signals to control the amplitudes of the signals fed to the respective loudspeakers to provide enhanced discrimination between front and rear signals. As described the matrixed input signals L T and R T include respectively the left front Lf and right front Rf signals together with both rear signals L b and R b , with the signals L b and R b in one input signal being in quadrature with the same signals in the other input signal, but with L b in one input leading the L b in the other input and R b in the one input lagging the R b in the other input, Fig. 2 (not shown). The signal L T is applied to phase shifting circuits 212, 222 which produce at their outputs signals having a phase difference of 90 degrees. Similarly the R T signal is applied to phase shifting circuits 242, 232 to produce signals having a phase difference of 90 degrees, and these signals directly, or after combination in adders, produce output signals L<SP>11</SP> F , L<SP>11</SP> B , R<SP>11</SP> F , R<SP>11</SP> B , in which the original signals L F , L B , R F , R B respectively predominate. Each phase shifter includes a respective transistor phase splitter 213, 223, &c., from which the signals L T and R T may be taken either in their original phase or phase inverted, and from these signals gain controlling signals L T +R T and L T -R T are derived to feed rectifiers 254, 256 and difference circuit 258. The arrangement is such that a front centre signal gives a predominant L T +R T signal and a rear centre signal gives a predominant L T - R T signal and these conditions are used to control the gain of amplifiers 215, 225, 235, 245, so that a front centre signal differentially increases the gain of the amplifiers feeding the front loud-speakers and a rear centre signal differentially increases the gain of the amplifiers feeding the rear loudspeakers.