Patent GB-1416631-A (GB)
Title: Discrete 4-channel stereo recording and/or reproducing system
IPC: H04S3/00
Filed: 1973-05-29
Abstract: 1416631 Quadraphonic system NIPPON COLUMBIA CO Ltd 29 May 1973 [30 May 1972 (2) 8 June 1972 (3) 15 June 1972] 25332/73 Heading H4R In a quadraphonic recording and reproducing system all four original signals are recorded on both channels of the record, with appropriate phase displacement and amplitude adjustment, while at least the original signals of each side modulate respective carriers which are added to the respective audio frequency signals on the two recording channels. The arrangement allows the recording to be reproduced by either a regulator matrix type decoder, a CD4 decoder, or a special decoder which is also suitable for reproduction of a CD4 signal or, with a simple switching which can be automatic on non- detection of a carrier signal, a regular matrix signal. Fig. 9, shows one embodiment of a coding system in which the left front L F  and right front R F  signals are recorded directly on the respective channels T L  and T R  together with a minor proportion " m " of the opposite front signals R F  and L F  respectively, the whole of the back signals of the respective side L B  and R B , after phase shifting in opposite directions, and a proportion of the back signals of the opposite sides R B  and L a  after phase shifting in opposite directions and phase invertion. In a similar fashion adders 13 and 23 produce composite signals which are the same as the signals T L  and T R , except that the back components are in each case inverted, and these signals modulate respective carriers from generator 10 to produce carrier signals C L  and C R  which are added to the respective base band signals T L  and T R  for recording on the two channels of the recording medium. For reproduction the base signals and carrier signals are separated by filters the carriers C L  and C R  are demodulated by detectors 35 and 45 and the four signals combined in the adders 32, 33, 42, 43, as shown, to provide the signals L B <SP>1</SP>, L F <SP>1</SP>, R F <SP>1</SP> and R B <SP>1</SP> to be fed to the reproducers. Vector diagrams are described, Figs. 11 to 13 (not shown) which show the reproduced signals with the regular matrix or DC4, decoders fed by signals coded by the coder of Fig. 9, or the CD4 signals as decoded by the decoder of Fig. 10, with alternative values of phase shift #. In a modification of the coder of Fig. 9, the carrier signals only carry information from signals on a respective side, i.e. in the coder of Fig. 9, the outputs of attenuators 52 and 56 are disconnected together with the connections between attenuators 54 and 58 and the respective adders 23 and 13. The decoder for such'a signal is similar to that of Fig. 10, with the connections from attenuators 62 and 66 broken. The resulting system gives improved reproduction of the CD4 system signal particularly when the phase shift applied to the two decoded rear signals is 22À5 degrees. In such a system the phase shift applied to the rear signals in the coder should be 45 degrees for best separation of the signals on reproduction. With such a system a different matrix, or alternative connections to the matrix, is required for reproduction of signals encoded by the regular matrix system. In Fig. 20 (not shown) the changeover of connections to the decoding matrix is effected by detection of the carrier signals on the CD4 or system according to the invention.