Systems for recording and/or reproducing four channel record disks having mixed sum and difference signals recorded on opposite groove walls

Claim 2

A recording system for a four channel record disk comprising: signal source means for supplying separate first, second, third, and fourth channel signals; matrix circuit means for forming a first sum signal and a first difference signal from said first and second channel signals and a second sum signal and a second difference signal from said third and fourth channel signals; compressor means for compressing said first and second difference signals only in the vicinity of a specific frequency, the output level of said compressor means being intensified as the input signal level thereto is decreased; angle-modulation means responsive to signals which have passed through said compressor means for frequency modulating said first and second difference signals up to said specific frequency and for phase modulating at least one part of the frequencies above Said specific frequency so that said specific frequency becomes the transition point of the modulation modes where frequency modulation changes to phase modulation thereby to produce first and second angle-modulated difference signals; mixing means for mixing said first and second sum signals respectively with said first and second anglemodulated difference signals; and recording means responsive to the resulting outputs of said mixing means respectively for recording by cutting on the left and right walls of a groove on the record disk.

Claim 3

A recording system as set forth in claim 1 in which said angle-modulating means phase modulates said first and second difference signals in the frequency range above said specific frequency.

Claim 4

A recording system as set forth in claim 1 and means whereby said angle-modulating means phase modulates signal components of the frequencies of said first and second difference signals in a band between a first specific frequency and a second specific frequency which is higher than said first specific frequency, and means whereby said angle-modulating means frequency modulates signal components of the frequencies in the range above said second specific frequency.

Claim 5

A recording system as set forth in claim 1 in which said compressor means comprises: frequency characteristic changing circuit means operating in response to an applied control signal voltage to intensify the levels of signals at and in the vicinity of said specific frequency; band-pass filter means for obtaining said signals at and in the vicinity of said specific frequency responsive to the output signals of said frequency characteristic changing circuit means; and control circuit means operating in response to the level of an output signal of said band-pass filter means to form a control signal voltage for controlling said frequency characteristic changing circuit means.

Claim 6

A recording system as set forth in claim 1 in which said specific frequency is of the order of 800 Hz.

Claim 9

A reproducing system as set forth in claim 6 in which said expandor means comprises: frequency characteristic changing circuit means operating in response to an applied control signal voltage to attenuate the levels of the frequency components of said demodulated first and second difference signals having frequencies in the vicinity of said specific frequency; band-pass filter means responsive to the demodulated first and second difference signals for passing frequency components thereof in the vicinity of said specific frequency; and control circuit means operating in response to the level of the output signal of said band-pass filter means to form a control signal voltage for controlling said frequency characteristic chanGing circuit means.

Claim 10

A reproducing system as set forth in claim 6 in which said specific frequency is of the order of 800 Hz.

Claim 13

A recording system for a four channel record disk comprising signal source means for supplying separate first, second, third and fourth channel signals; matrix circuit means operated responsive to said channel signals for composing a first sum signal and a first difference signal from the first and second channel signals and also for composing a second sum signal and a second difference signal from the third and fourth channel signals; compressor means for compressing the first difference signal and the second difference signal respectively with particular compression emphasis on first frequency components which are distributed at and in the vicinity of a predetermined frequency and with less than said particular compression emphasis in second frequency components in a range which is lower than the first frequency components, said particular compression emphasis being further increased as the level of said first frequency components decreases in said range; angle-modulation means for phase modulating a carrier signal responsive to third frequency components of the compressed first difference signal and the compressed second difference signal respectively which frequency components are within a frequency band, the lowest frequency of which is said predetermined frequency, and said angle-modulation means frequency modulating the carrier signal responsive to frequency components of the compressed first difference signal and the compressed second difference signal respectively, which are frequency components outside of said frequency band, thereby producing a first angle-modulated difference signal and a second angle-modulated difference signal respectively; mixing means for mixing and multiplexing the first sum signal with the first angle-modulated difference signal and also the second sum signal with the second angle-modulated difference signal respectively; and recording means for simultaneously recording one of the multiplexed signals on the left wall of a groove of a record disk and the other multiplexed signal on the right wall of the groove.

Claim 14

A recording system for a four channel record disk comprising signal source means for supplying separate first, second, third and fourth channel signals; matrix circuit means operated responsive to said channel signals for composing a first sum signal and a first difference signal from the first and second channel signals and also for composing a second sum signal and a second difference signal from the third and fourth channel signals; compressor means for compressing the first difference signal and the second difference signal respectively with particular compression emphasis on first frequency components which are distributed at and in the vicinity of a predetermined frequency and with less than said particular compression emphasis in second frequency components in a range which is lower than the first frequency components, said particular compression emphasis being further increased as the level of said first frequency components decreases in said range; angle-modulation means for phase modulating a carrier signal responsive to third frequency components of the compressed first difference signal and the compressed second difference signal respectively which frequency components are within a frequency band, the lowest frequency of which is said predetermined frequency, and said angle-modulation means frequency modulating the carrier signal responsive to frequency components of the compressed first difference signal and the compressed second difference signal respectively, which are frequency components outside of said frequency band, thereby producing a first angle-modulated difference signal and a second angle-modulated difference signal respectively; mixing means for mixing and multiplexing the first sum signal with the first angle-modulated difference signal and also the second sum signal with the second angle-modulated difference signal respectively; and recording means for simultaneously recording one of the multiplexed signals on the left wall of a groove of a record disk and the other multiplexed signal on the right wall of the groove.

Claim 15

The recording system as defined in claim 10 wherein each of said compressor means comprises frequency characteristic changing circuit means operated responsive to a control signal for further intensifying said first frequency components as compared to the second low frequency components of the corresponding difference signal as the level of said control signal decreases; band-pass filter means for filtering and obtaining said frequency components of the corresponding difference signal from the output signal of said frequency characteristic changing circuit means; and control circuit mEans for producing the control signal in accordance with the level of the output signal of said band-pass filter means.

Claim 16

The recording system as defined in claim 10 wherein said predetermined frequency is approximately equal to 800 Hz.

Claim 17

A reproducing system for a four channel record disk having respectively recorded thereon a multiplexed signal of the first sum signal and the first angle-modulated difference signal and the multiplexed signal of a second sum signal and a second angle-modulated difference signal; said reproducing system comprising separating means for separating the first sum signal, the first angle-modulated difference signal, the second sum signal and the second angle-modulated difference signal from the multiplexed signals picked up from the left and right walls of the groove of the record disk; angle-demodulation means for angle-demodulating the angle-modulated difference signals to reproduce the compressed first difference signal and the compressed second difference signal respectively; expandor means for expanding the reproduced compressed first difference signal and the reproduced compressed second difference signal respectively to attenuate the first frequency components distributed at said predetermined frequency with particular expansion emphasis, with less than said particular expansion emphasis in the second frequency components of the reproduced signals, said particular expansion emphasis being further increased as the level of said first frequency components decreases in said range, so as to restore the original first difference signal and the original second difference signal respectively; and matrix means responsive to the separated first sum signal and the restored first difference signal, and also responsive to the separated second sum signal and the restored second difference signal respectively for individually reproducing the original first, second, third and fourth channel signals.

Claim 18

A reproducing system for a four channel record disk having respectively recorded thereon a multiplexed signal of the first sum signal and the first angle-modulated difference signal and the multiplexed signal of a second sum signal and a second angle-modulated difference signal; said reproducing system comprising separating means for separating the first sum signal, the first angle-modulated difference signal, the second sum signal and the second angle-modulated difference signal from the multiplexed signals picked up from the left and right walls of the groove of the record disk; angle-demodulation means for angle-demodulating the angle-modulated difference signals to reproduce the compressed first difference signal and the compressed second difference signal respectively; expandor means for expanding the reproduced compressed first difference signal and the reproduced compressed second difference signal respectively to attenuate the first frequency components distributed at said predetermined frequency with particular expansion emphasis, with less than said particular expansion emphasis in the second frequency components of the reproduced signals, said particular expansion emphasis being further increased as the level of said first frequency components decreases in said range, so as to restore the original first difference signal and the original second difference signal respectively; and matrix means responsive to the separated first sum signal and the restored first difference signal, and also responsive to the separated second sum signal and the restored second difference signal respectively for individually reproducing the original first, second, third and fourth channel signals.

Claim 19

The reproducing system as defined in claim 13 wherein each of said expandor means comprises frequency characteristic changing circuit means operating responsive to a control signal for further attenuating said first frequency components as compared to the second low frequency components of the corresponding reproduced compressed difference signal as the level of said control signal decreases; band-pass filter means for filtering and obtaining said first frequency components from the corresponding reproduced compressed difference signal which frequency components are distributed at and in the vicinity of said predetermined frequency; and control circuit means for producing said control signal in accordance with the level of the output signal of said band-pass filter means.