Patent GB-1400061-A (GB)
Title: Multisignal transmission apparatus
IPC: H04S3/02
Filed: 1972-07-10
Abstract: 1400061 Quadraphonic systems SONY CORP 10 July 1972 [19 July 1971] 32143/72 Heading H4R In a four channel decoder, variable mixing circuits are provided between the channels and are controlled by cross-talk components to substantially cancel the cross-talk components. Composite input signals L T  and R T  (Fig. 2) having phasor groups 38, 40 are applied to input terminals 50,52. Signal L T  is applied to an all-pass phase shift network 54 while signal R T  is applied to an all-pass phase shift network 56. # is a function of frequency, 0À707 of the output signals of networks 54, 56 are differenced at junction 6 and are summed at junction 62. Amplifiers 58, 62, 66 and 60 are provided for the four derived signals. Phase inverters 80, 82 reverse the outputs of amplifiers 60, 66. Further phase shift networks 88, 90, 92, 94 are provided together with phase inverters 96, 98. The output terminals provide dominant signals L f , L b , R b  and R f  in phase, together with cross-talk components. Signals at different points along the decoder are shown by phasor groups. The 0À707 Lb signal of phasor group 68 and the 0À707 Lb signal of phasor group 74 are out of phase with each other. A mixing circuit 120 (Fig. 4) is controlled to cancel the 0À707 Lb signals and comprises a transistor T, having collector and emitter electrodes connected to the outputs of amplifiers 58 and 60 respectively. The base has a terminal 120a for application of a control signal. Similar mixing circuits 122, 124 and 126 are controlled to cancel 0À707 R f  signals, 0À707 R b  signals, 0À707 R f  signals respectively. This is effected by a cross-talk signal detecting circuit 130 (Fig. 3) which supplies the mixing circuits 120, 122, 124, 126. Input terminals 132, 134, 136, 137 of circuit 130 are connected to output terminals 132a, 134a, 136a and 137a (Fig. 2) so that phasor group signals 68, 70, 72, 74 are supplied to all-wave rectifier circuits 138, 140, 142, 144. Their output signals 146, 150, 152, 148 are supplied to subtracting circuits 154, 156, phase inverters 162, 168 and rectifiers 160, 164, 166, 170. Output terminals 160a, 164a, 166a and 170a, which provide control signals, are connected to input terminals 126a, 122a, 120a and 124a respectively (Fig. 2). Considering the L f  signal only, this is required at output terminal 112 (Fig. 2) but not at output terminals 114, 116. The D.C. component of the L f  signal (control signal α) is obtained at output terminals 160a (Fig. 3) and supplied to the input terminals 126a of mixing circuit 126 as the control signal. The transistor T, of mixing circuit 126 thereby becomes conductive between emitter and collector and phasor group signals 70, 86 are mixed in circuit 126 to cancel the 0À707 L f  signals which are out of phase. Other unwanted signals are cancelled in similar manner. Fig. 8 (not shown) shows a decoder for composite input signals L T , R T  having phasor groups different from those of Fig. 2. The decoder is of simpler form but centre front signals and centre rear signals may be added to the input signals L T  and R T  by a circuit (Fig. 9, not shown) connected to the decoder. Only two mixing circuits (360, 362) are required and each may be similar to the circuit of Fig. 4. The Fig. 9 circuit may, if desired, by used in conjunction with Fig. 2. Yet another decoder (Fig. 10, not shown) is for use with composite signals L T , R T  as shown by phasor groups on the Figure. It includes a basic matrix circuit (406) and four mixing circuits (480, 482, 484, 486) of the type shown in Fig. 4. It requires a crosstalk signal detection circuit (Fig. 11, not shown) using full wave rectifiers, substracting junctions, &c. but is different from that of Fig. 2.