Four-Channel Stereophonic Sound Reproducing System

Claim 2

A four-channel stereophonic sound reproducing system for reproducing four individual audio information signals on four separate loudspeakers adapted to be arranged around a listener, said four individual audio information signals corresponding to four original signals generated from four separate microphones respectively placed at left front, right front, left rear and right rear of the listener, said four original signals being contained in encoded first and second composite signals L and R which are defined by the following equations: L (Lf+jLb) cos theta + (Rf+jRb) sin theta R (Rf-jRb) cos theta + (Lf-jLb) sin theta where Lf left front, Rf right front, Lb left rear and Rb right rear; said sound reproducing system comprising: first and second input terminals to which said first and second composite signals L and R are respectively applied; a decpder matrix circuit connected to said input terminals and combining said first and second composite signals L and R to derive four reproduced signals Lf1, Rf1, Lb1and Rb1which are defined by the following equations: Lf1 L cos theta + R sin theta Rf1 R cos theta + L sin theta Lb1 L cos theta - sin theta Rb1 R cos theta - L sin theta a sensor circuit for producing at least one of four judgment signals C1, C2, C3and C4as a function of said reproduced signals Lf1, Rf1, Lb1and Rb1, said sensor circuit having first, second, third and fourth level detectors respectively detecting the level of said four reproduced signals Lf1, Rf1, Lb1and Rb1; a first mixer connected to receive the outputs of said first and third level detectors for producing a sum of the signal levels of the outputs of said first and third level detectors; a second mixer connected to receive the outputs of said third and fourth level detectors for producing a sum of the signal levels of the outputs of said third and fourth level detectors; a third mixer connected to receive the outputs of said second and fourth level detectors for producing a sum of the signal levels of the outputs of said second and fourth level detectors; a fourth mixer connected to receive the outputs of said first and second level detectors for producing a sum of the signal levels of the outputs of said first and second level detectors; a first level comparator having negative and positive input terminals for respectively receiving the outputs of said first and third mixers at an amplitude ratio of 1/(1+ square root 2) :1 to produce said first judgment signal C1; a second level comparator having positive and negative input terminals for respectively receiving the outputs of said first and third mixers at an amplitude ratio of 1:1/(1+ square root 2) to produce said second judgment signal C2; a third level comparator having positive and negative input terminals for respectively receiving the outputs of said second and fourth mixers at an amplitude ratio of 1:1/(1+ square root 2) to produce said third judgment signal C3; and a fourth level comparator having negative and positive input terminals for respectively receiving the outputs of said second and fourth mixers at an amplitude ratio of 1/(1+ square root 2):1 to produce said fourth judgment signal C4; and a controller circuit for controlling the respective levels of the four reproduced signals Lf1, Rf1, Lb1and Rb1from said decoder matrix circuit in response to the four judgment signals C1 to C4 from said sensor circuit, to provide four audio information signals Lf2, Rf2, Lb2 and Rb2 having decreased cross-talk between adjacent channels.

Claim 3

A four-channel sterophonic sound reproducing system according to claim 1 wherein: said sensor circuit further comprises a fifth level comparator having positive and negative input terminals for respectively receiving the outputs of said second and third level detectors at an amplitude ratio of 1:1 to produce a fifth judgment signal C5; and a sixth level comparator having positive and negative input terminals for respectively receiving the outputs of said forst and fourth level detectors at an amplitude ratio of 1:1 to produce a sixth judgment signal C6; and said controller circuit comprises a first amplitude control signal generator connected to receive said first, fourth and fifth judgment signals for producing a first control signal in response to the lowest level signal of said first, fourth and fifth judgment signals; a second amplitude control signal generator connected to receive said second, fourth and sixth judgment signals for producing a second control signal in response to the lowest level signal of said second, fourth and sixth judgment signals; a third amplitude control signal generator connected to receive said second, third and fifth judgment signals for producing a third control signal in response to the lowest level signal of said second, third and fifth judgment signals; a fourth amplitude control signal generator connected to receive said first, third and sixth judgment signals for producing a Fourth control signal in response to the lowest level signal of said first, third and sixth judgment signals; a first amplitude controller coupled to the output of said first amplitude control signal generator and operative to attenuate the level of said reproduced signal Lf1 to substantially zero when the level of said first control signal is lower than a predetermined value and to amplify said reproduced signal Lf1 when the level of said first control signal is higher than said predetermined value so as to obtain the first audio information signal Lf2; a second amplitude controller coupled to the output of said second amplitude control signal generator and operative to attenuate the level of said reproduced signal Rf1 to substantially zero when the level of said second control signal is lower than a predetermined value and to amplify said reproduced signal Rf1 when the level of said second control signal is higher than said predetermined value so as to obtain the second audio information signal Rf2; a third amplitude controller coupled to the output of said third amplitude control signal generator and operative to attenuate the level of said reproduced signal Lb1 to substantially zero when the level of said third control signal is lower than a predetermined value and to amplify said reproduced signal Lb1 when the level of said third control signal is higher than said predetermined value so as to obtain the third audio information signal Lb2; and a fourth amplitude controller coupled to the output of said fourth amplitude control signal generator and operative to attenuate the level of said reproduced signal Rb1 to substantially zero when the level of said fourth control signal is lower than a predetermined value and to amplify said reproduced signal Rb1 when the level of said fourth control signal is higher than said predetermined value so as to obtain the fourth audio information signal Rb2.

Claim 4

A four-channel stereophonic sound reproducing system according to claim 1 wherein first and second phase shifters are respectively connected between said first and second input terminals and said decoder matrix circuit, said first phase shifter including four output terminals for obtaining four signals P1, P2, P3 and P4 respectively having phase differences - pi /2, 0, pi /2 and pi with respect to the first composite signal L; and said second phase shifter including four output terminals for obtaining four signals Q1, Q2, Q3 and Q4 respectively having phase differences - pi /2, 0, pi /2 and pi with respect to the second composite signal R; and wherein: said decoder matrix circuit includes eight input terminals of receiving said respective signals P1 to P4 and Q1 to Q4, and sixteen output terminals for providing sixteen signals Lb1, Lb1j, -Lb1j, -Lb1, Lf1, Lf1j, - Lf1j, -Lf1, Rf1, Rf1j, -Rf1j, -Rf, Rb1, Rb1j, -Rb1j, and -Rb1; and said controller circuit includes a first mixer connected to receive said signals Lf1j and -Rb1; a second mixer connected to receive said signals -Lb1j and -Rf1; a third mixer connected to receive said signals -Lf1 and Rb1j; a fourth mixer connected to receive said signals -Rf1j and -Lb1; a first amplitude controller coupled to the output of said first mixer for controlling the output of said first mixer in response to said judgment signal C5; a second amplitude controller coupled to the output of said second mixer for controlling the output of said second mixer in response to said judgment signal C6; a third amplitude controller coupled to the output of said third mixer for controlling the output of said third mixer in response to said judgment signal C5; a fourth ampLitude controller coupled to the output of said fourth mixer for controlling the output of said fourth mixer in response to said judgment signal C6; a fifth amplitude controller for controlling said signal -Lb1j in response to said judgment signal C1; a sixth amplitude controller for controlling said signal -Lf1j in response to said judgment signal C4; a seventh amplitude controller for controlling said signal -Rf1j in response to said judgment signal C2; and eighth amplitude controller for controlling said signal -Rb1j in response to said judgment signal C3; ninth, tenth, eleventh and twelfth amplitude controllers for controlling said signals Lb1j, Lf1j, Rf1j and Rb1j in response to said judgment signals C4, C3, C2 and C1, respectively; a fifth mixer connected to receive said signal Lb1 and the output signals of said first, seventh and eleventh amplitude controllers; a sixth mixer connected to receive said signal Lf1 and the output signals of said second, eighth and twelfth amplitude controllers; a seventh mixer connected to receive said signal Rf1 and the output signals of said third, fifth and ninth amplitude controllers; an eighth mixer connected to receive said signal Rb1 and the output signals of said fourth, sixth and tenth amplitude controllers; a first amplitude control signal generator connected to receive said judgment signals C1 and C4; a second amplitude control signal generator connected to receive said judgment signals C2 and C4; a third amplitude control signal generator connected to receive said judgment signals C2 and C3; a fourth amplitude control signal generator connected to receive said judgment signals C1 and C3; thirteenth, fourteenth, fifteenth and sixteenth amplitude controllers for controlling the output signals of said fifth to eighth mixers in response to the control signals generated from said first to fourth amplitude control signal generators respectively so as to obtain said four audio information signals Lb2, Lf2, Rf2, Rb2.

Claim 5

A four-channel stereophonic sound reproducing system according to claim 1 wherein: said decoder matrix circuit further comprises first, second, third and fourth output terminals for obtaining four control channel information signals Fc1, Bc1, and Rc1 which are expressed by the following equations: Fc1 1/ Square Root 2L + 1/ Square Root 2R Bc1 -1/ Square Root 2L + 1/ Square Root 2R Lc1 L Rc1 R and said controller circuit comprises first, second, third and fourth factor multipliers for multiplying said four signals Fc1 to Rc1 by a factor of 0.383, respectively; first, second, third and fourth amplitude controllers connected to receive said four signals Fc1 to Rc1 to control them in response to said judgment signals C1 to C4, respectively; fifth, sixth seventh and eighth amplitude controllers connected to receive the output signals of said first to fourth factor multipliers to control them in response to judgment signals C1 to C4, respectively; a first mixer connected to receive said signal Lb1 and the output signals of said first, third, sixth and eighth amplitude controllers; a second mixer connected to receive said signal Lf1 and the output signals of said second, third, fifth and eighth amplitude controllers; a third mixer connected to receive said signal Rf1 and the output signals of said second, fourth, fifth and seventh amplitude controllers; a fourth mixer connected to receive said signal Rb1 and the output signal of said first, fourth, sixth and seventh amplitude controllers; and first, second, third and fourth phase shifters for shifting the respective phases of the outputs from said first to fourth mixers to form said output signals Lb2, Lf2, Rf2 and Rb2.

Claim 6

A fouR-channel stereophonic sound reproducing system according to claim 1 wherein: said decoder matrix circuit further comprises first, second, third and fourth output terminals for obtaining four control channel information signals Fc1, Bc1, Lc1 and Rc1 which are expressed by the following equations: Fc1 1/ Square Root 2L + 1/ Square Root 2R Bc1 1/ Square Root 2L + 1/ Square Root 2R Lc1 R Rc1 R and said controller circuit comprises first, second, third and fourth amplitude controllers for controlling the amplitudes of said four control channel information signals Fc1 to Rc1 in response to said judgment signals C1 to C4, respectively; a first mixer connected to receive said signal Lb1 and the output signals of said first and fourth amplitude controllers; a second mixer connected to receive said signal Lf1 and the output signals of said second and fourth amplitude controllers; a third mixer connected to receive said signal Rf1 and the output signals of said second and third amplitude controllers; a fourth mixer connected to receive said signal Rb1 and the output signals of said first and third amplitude controllers; first, second, third and fourth resistors having respective input and output terminals, the input terminals of said first, second, third and fourth resistors being respectively coupled to the output terminals of said first to fourth mixers; first and second variable resistors, said first variable resistor being coupled across the output terminals of said second and third resistors and said second variable resistor being coupled across the output terminals of said first and fourth resistors, said first and second variable resistors having respective first and second movable terminals for receiving said respective judgment signals C1 and C2; first and second inverters respectively connected to the output terminals of said first and fourth resistors; first and second buffer circuits respectively connected to the output terminals of said second and third resistors; fifth, sixth, seventh and eighth resistors having respective input and output terminals, the input terminals of said fifth, sixth, seventh and eighth resistors being respectively coupled to the output terminals of said first and second inverters and said first and second buffer circuits; third and fourth variable resistors, said third variable resistor being coupled across the output terminals of said fifth and sixth resistors, and said fourth variable resistor being coupled across the output terminals of said seventh and eighth resistors, said third and fourth variable resistors having respective third and fourth movable terminals for receiving said respective judgment signals C3 and C4; and first, second, third and fourth phase shifters for shifting the respective phases of the outputs obtained from the output terminals of said fifth to eighth resistors to form output signals Lb3, Lf3, Rf3 and Rb3.

Claim 7

A four-channel stereophonic sound reproducing system according to claim 1 wherein first and second phase shifters are respectively connected between said first and second input terminals and decoder matrix circuit, said first phase shifter including four output terminals for obtaining four signals P1, P2, P3 and P4 respectively having phase differences - pi /2, 0, pi /2 and pi with respect to the first composite signal L; and said second phase shifter including four output terminals for obtaining four signals Q1, Q2, Q3 and Q4 respectively having phase differences - pi /2, 0, pi /2 and pi with respect to the second composite signal R; and wherein: said decoder matrix circuit includes eight input terminals for receiving said respective signals P1 to P4 and Q1 to Q4, and eight output terminals for providing eigHt signals Lb1, Lb1j, -Lb1j, Lf1, Rf1, Rb1, -Rb1j and Rb1j; said sensor circuit further includes fifth and sixth level detectors for detecting the levels of said respective signals Lb1j and -Rb1j; and a fifth mixer having first and second negative input terminals for respectively receiving the output signals of said fifth and sixth level detectors and having first and second positive input terminals for respectively receiving the output signals of said first and second level detectors, the amplitude ratio between the output signal of the fifth or sixth level detector and that of the first or second level detector being set at 1:1/(1+ Square Root 2) so as to obtain a single judgment signal C corresponding to said first judgment signal C1; and said controller circuit comprises a first amplitude controller connected to receive said signal -Lb1j and said judgment signal C; a second amplitude controller connected to receive said signal Rb1j and said judgment signal C; a third amplitude controller connected to receive said signal Lb1 and said judgment signal C and to generate said third audio information signal Lb2; a fourth amplitude controller connected to receive said signal Rb1 and said judgment signal C and to generate said fourth audio information signal Rb2; a sixth mixer connected to receive said signal Lf1 and the output signal of said second amplitude controller and to generate said first audio information signal Lf2; and a seventh mixer connected to receive said signal Rf1 and the output signal of said first amplitude controller and to generate said second audio information signal Rf2.

Claim 8

A four-channel stereophonic sound reproducing system according to claim 1 wherein: said sensor circuit further includes a fifth mixer having first and second positive input terminals and third and fourth negative input terminals for respectively receiving the output signals of said first to fourth level detectors, the amplitude ratio between the output signal of the third or fourth level detector and that of the first or second level detector being set at 1:1/(1+ Square Root 2) so as to obtain a signal judgment signal C corresponding to said first judgment signal C1; and said controller circuit includes a first amplitude controller for controlling the amplitude of the signal Lf1 in response to the judgment signal C; a second amplitude controller for controlling the amplitude of the signal Rf1 in response to the judement signal C; a sixth mixer having positive and negative input terminals for mixing the signal Lf1 and the output signal of the second amplitude controller at an amplitude ratio of 1: 1/ Square Root 2; a seventh mixer having positive and negative input terminals for mixing the signal Rf1 and the output signal of the first amplitude controller at an amplitude ratio of 1: 1/ Square Root 2; third, fourth, fifth and sixth amplitude controllers for respectively controlling the amplitudes of the output signals of said sixth and seventh mixers and of the signals Lb1 and Rb1 in response to said judgment signal C so as to obtain said first through fourth audio information sigals Lf2, Rf2, Lb2 and Rb2.