Patent GB-1476772-A (GB)
Title: Decoding apparatus for reproducing four separate audio information signals
IPC: H04S3/02
Filed: 1974-11-27
Abstract: 1476772 Quadraphonic matrix decoders SONY CORP 27 Nov 1974 [29 Nov 1973] 51420/74 Heading H4R In a matrix quadraphonic decoder in which two input signals each containing at least three out of four information signals are decoded to produce four output signals each containing a respective predominant signal and a different pair of subdominant signals, the magnitudes of at least two of the output signals are compared to develop a control signal which is used to vary the time delay of variable delay circuits in the output channels. By providing differential delay in the output signals a sound is localized to the position of the source from which it is first heard. As shown in Fig. 2 an SQ matrix circuit 34 produces four output signals LF<SP>1</SP>, RF<SP>1</SP>, LB<SP>1</SP>, and RB<SP>1</SP> which are applied via respective delay circuits, formed by charge transfer devices, to the output transducers 131, 132, 133, 134. In addition the matrix circuit outputs are fed through gain control amplifiers 70, 72, 74, 76, full wave rectified, and the LF<SP>1</SP> and RF<SP>1</SP> signals are compared and the difference signal fed to a clipping or slicing circuit 96 which provides an output if the difference between the LF<SP>1</SP> and RF<SP>1</SP> signals exceeds a predetermined amount. Similarly the LB<SP>1</SP> and RB<SP>1</SP> signals are compared and a slicing circuit 98 provides an output if the difference exceeds a predetermined amount. The slicing circuits outputs are fed to respective inputs of a differential amplifier 94 having opposite polarity outputs which are used to control the frequency of oscillators 108 and 109 driving clock generators 110 and 111 which control the stepping of the charge transfer delay devices to differentially vary the delay in the LF<SP>1</SP> and FR<SP>1</SP> channels relative the delay in the LB<SP>1</SP> and RB<SP>1</SP> channels. The arrangement is such that if front signals predominate LB<SP>1</SP> and RB<SP>1</SP> both contain cross talk components LF and RF together with the respective predominant LB and RB components the difference between LB<SP>1</SP> and RB<SP>1</SP> will therefore be low while the difference between LF<SP>1</SP> and RF<SP>1</SP> would be finite and a positive output would occur at 106 on the logic circuit output and this would reduce the delay given to the LF<SP>1</SP> and RF<SP>1</SP> signals and increase the delay given to the LB<SP>1</SP> and RB<SP>1</SP> signals. With back signals predominanting the cross talk components LB and RB in both the front signals LF<SP>1</SP> and RF<SP>1</SP> would make the difference between LF<SP>1</SP> and BF<SP>1</SP> low, # LB<SP>1</SP> | - | RB<SP>1</SP> # would be finite, and the delays on LB<SP>1</SP> and RB<SP>1</SP> would be reduced and on LF<SP>1</SP> and RF<SP>1</SP> they would be increased. In a modification, Fig. 5 (not shown), the outputs from differential amplifier 94 are used to control the gain of amplifiers (142, 143, 144, and 145) interposed between the variable delays 117, 118, 119, 120, and the transducers 131, 132, 133, 134, and differentiating circuits (146, 147) are provided in the feed to the variable frequency oscillators 108 and 109 so that the variable delay is only implemented at the commencement of a sound. It is also suggested that the arrangement could be applied to an RM (regular matrix) system by comparing LF<SP>1</SP> and KB<SP>1</SP> signals and BF<SP>1</SP> and LB<SP>1</SP> signals and delaying one pair relative the other.