Muting circuit

Claim 2

A muting circuit comprising a cascade of circuits including at least: input terminal means; means for detecting the level of a carrier wave component in an input signal appearing at said input terminal means; first time constant means having a first time constant characteristic for producing an output thereform with a first predetermined time constant in response to the detection of a predetermined signal strength level in the output of said level detecting means; second time constant means having a second time constant characteristic for producing an output thereof with a second time constant in response to the output of said first time constant means when a carrier wave component is detected at the input terminal means, the duration of said second time constant being longer than the duration of said first time constant, means for making said second time constant substantially zero when a carrier wave component is not detected by said level detecting means; third time constant means having a third time constant characteristic for producing an output therefrom with a third time constant in response to the output supplied from said second time constant means, the duration of said third time constant being longer than the duration of the second time constant; and means including a gate circuit coupled to said input terminal means and operating in response to the output signal supplied from said third time constant means to pass or block the input signal, said third time constant means holding said gate circuit in a conductive state to pass the signal during the period of time corresponding to the difference between the third and second time constants.

Claim 3

A muting circuit according to claim 1 which is incorporated in a multichannel disc demodulation system comprising means coupled to said input terminal means for selecting an angularly modulated carrier wave superimposed upon an unmodulated signal picked up from a multichannel disc, said level detecting means being coupled to said selecting means to detect the level of the angularly modulated carrier wave component reproduced from the multichannel disc, and means for controlling said gate circuit means responsive to the output of the third time constant means to switch between a conductive signal passing state and a non-conductive signal blocking state.

Claim 4

A muting circuit according to claim 1 which further comprises a first inverter means for switching "on-off" each time that the envelope waveform of the output signal of said first time constant means crosses a predetermined level, and a second inverter means for waveshaping and phase inverting the output signal of said first inverter.

Claim 5

A muting circuit according to claim 3 which further comprises a third inverter means connected to said second time constant means.

Claim 6

A muting circuit according to claim 3 which further comprises a NAND gate circuit means connected to said second time constant means, said NAND gate operating to cause the time constant of the second time constant means to be substantially zero when said NAND gate is in its "off" state.

Claim 7

A muting circuit according to claim 1 which further comprises a waveshaping circuit means connected to said third time constant means.

Claim 8

A muting circuit according to claim 1 in which the third time constant means is set at a value which is a longer time constant than the sum of the second time constant and the acceptable duration of interruptions in the carrier wave component of a normal input signal, and the third time constant means holds "on" the muting gate circuit while an input signal drops out for a period of time which is less than the third time constant.

Claim 9

A muting circuit according to claim 1 in which the first time constant has a duration measured in terms of tens of microseconds, the second time constant has a duration in the order of approximately 0.2 seconds, and the third time constant has a duration in the order of approximately 0.2 to 0.3 seconds.

Claim 10

A muting circuit comprising a plurality of circuit connected in cascade, said cascade comprising at least the following: means for detecting the level of a carrier wave component in an input signal; a first time constant circuit means responsive to said detecting means for producing an output in a waveform having a rising and falling time constant τ 1 ; a second time constant circuit means responsive to said first time constant circuit means for producing an output in a waveform rising with a time constant τ 2 which is longer than the time constant τ 1 and falling with a time constant which is shorter than constant τ 1 ; a third time constant circuit means responsive to said second time constant circuit means for producing an output in a waveform which falls after a predetermined delay time, corresponding to the time constant τ 2 , following the start of the rise of the output of the second time constant circuit means, the output wave of the third time constant circuit means rising with a time constant τ 3 which is longer than the time constant τ 2 following the falling of the output of the second time constant circuit means; and gate circuit means connected to receive the input signal and to be controlled responsive to the output of the third time constant circuit means, said gate circuit means passing the input signal responsive to the falling edge of the output waveform of the third time constant circuit means, and preventing the passing of the input signal with a delay of a time corresponding to the time constant τ 3 , said gate being placed in said non-passing condition responsive to the rising edge of the output of the third time constant circuit means.

Claim 11

A muting circuit comprising a plurality of circuit connected in cascade, said cascade comprising at least the following: means for detecting the level of a carrier wave component in an input signal; a first time constant circuit means responsive to said detecting means for producing an output in a waveform having a rising and falling time constant τ 1 ; a second time constant circuit means responsive to said first time constant circuit means for producing an output in a waveform rising with a time constant τ 2 which is longer than the time constant τ 1 and falling with a time constant which is shorter than constant τ 1 ; a third time constant circuit means responsive to said second time constant circuit means for producing an output in a waveform which falls after a predetermined delay time, corresponding to the time constant τ 2 , following the start of the rise of the output of the second time constant circuit means, the output wave of the third time constant circuit means rising with a time constant τ 3 which is longer than the time constant τ 2 following the falling of the output of the second time constant circuit means; and gate circuit means connected to receive the input signal and to be controlled responsive to the output of the third time constant circuit means, said gate circuit means passing the input signal responsive to the falling edge of the output waveform of the third time constant circuit means, and preventing the passing of the input signal with a delay of a time corresponding to the time constant τ 3 , said gate being placed in said non-passing condition responsive to the rising edge of the output of the third time constant circuit means.

Claim 12

A muting circuit according to claim 9 which further comprises a first inverter means for producing an output which is switched "on" or "off" each time that an envelope of the waveform of the output signal of said first time constant circuit means crosses a predetermined level, and a second inverter means for shaping and inverting the wave of the output signal of said first inverter means.

Claim 13

A muting circuit according to claim 10 which further comprises a third inverter means connected to said second time constant circuit means.

Claim 14

A muting circuit according to claim 11 in which the third inverter means produces an output with a waveform falling with a time delay corresponding to the time constant τ 2 measured from the rising edge of the output of the second time constant circuit means and rising at substantially the instant of the falling of the output of the second time constant circuit means.

Claim 15

A muting circuit according to claim 9 which further comprises a wave-shaping circuit connected to said third time constant circuit means.

Claim 16

A muting circuit according to claim 9 in which the time constant τ 3 of said third time constant circuit means is a value which is greater than the sum of the time constant τ 2 of said second time constant circuit means and the duration of an interruption of the carrier wave component of a normal input signal, and the third time constant circuit means causes the gate circuit to pass signals with respect to an input signal drop out which is less than the time constant τ 3 .

Claim 17

A muting circuit according to claim 9 in which the time constant τ 1 of said first time constant circuit means is measured in terms of tens of microseconds, the time constant τ 2 of said second time constant circuit means being approximately 0.2 seconds, and the time constant τ 3 of said third time constant circuit means being in the range of 0.2 to 0.3 seconds.