Phase-lock-loop fm-stereo decoder including stereophonic/monophonic blend system for reducing audio distortion

Claim 2

In an FM-stereo decoder for demodulating a standard composite stereophonic signal including an L + R signal, an L - R modulated 38 KHz suppressed subcarrier signal, and a 19 KHz pilot signal; the combination comprising: means including a phase-lock-loop for generating a 38 KHz demodulating signal in phase synchronization with the 19 KHz pilot signal, the phase-lock-loop including a phase detector for producing an error voltage having an amplitude defined as a function of the phase difference between the 19 KHz pilot signal and the 38 KHz demodulating signal such that the amplitude of the error signal increases in response to shifts in the phase of the 19 KHz pilot signal caused by distorted reception; means including an audio decoder having L and R output channels for demodulating the L + R signal and the L - R modulated 38 KHz suppressed subcarrier signal in response to the 38 KHz demodulating signal to provide an L audio signal on the L output channel and an R audio signal on the R output channel; a coupling network including an electronic switch connected across the L and R output channels of the audio decoder for establishing the separation between the L and R output channels at substantially full channel separation when the electronic switch is turned off and for establishing the separation between the L and R output channels at less than full channel separation when the electronic switch is turned on; and a level detector responsive to an initial predetermined increase in the amplitude of the error voltage due to the initiation of distorted reception to substantially instantaneously turn on the electronic switch thereby to rapidly shift toward full monophonic operation for reducing the discernible audio distortion resulting from the distorted reception, the level detector including a timing network responsive to a subsequent predetermined decrease in the amplitude of the error voltage due to the termination of distorted reception to relatively gradually turn off the electronic switch thereby to slowly shift to full stereophonic operation for reducing the discernible audio disruption resulting from the shift back to full stereophonic operation.

Claim 3

In an FM-stereo decoder for demodulating a standard composite stereophonic signal including an L + R signal, an L - R modulated 38 KHz suppressed subcarrier signal, and a 19 KHz pilot signal; the combination comprising: means including a phase-lock-loop for generating a 38 KHz demodulating signal in phase synchronization with the 19 KHz pilot signal, the phase-lock-loop including a phase detector for producing an error voltage having an amplitude defined as a function of the phase difference between the 19 KHz pilot signal and the 38 KHz demodulating signal such that the amplitude of the error signal increases in response to shifts in the phase of the 19 KHz pilot signal Caused by distorted reception; means including an audio decoder having L and R output channels for demodulating the L + R signal and the L - R modulated 38 KHz suppressed subcarrier signal in response to the 38 KHz demodulating signal to provide an L audio signal on the L output channel and an R audio signal on the R output channel; a coupling network including an electronic switch connected across the L and R output channels of the audio decoder for establishing the separation between the L and R output channels at substantially full channel separation when the electronic switch is turned off and for establishing the separation between the L and R output channels at less than full channel separation when the electronic switch is turned on; and a level detector responsive to an initial predetermined increase in the amplitude of the error voltage due to the initiation of distorted reception to substantially instantaneously turn on the electronic switch thereby to rapidly shift toward full monophonic operation for reducing discernible audio distortion resulting from the distorted reception, the level detector including a timing network responsive to a subsequent predetermined decrease in the amplitude of the error voltage due to the termination of distorted reception to relatively gradually turn off the electronic switch thereby to slowly shift to full stereophonic operation for reducing the discernible audio disruption resulting from the shift to full stereophonic operation; the coupling network including a resistive element for establishing a minimum separation between the L and R output channels of the audio decoder when the electronic switch is turned on at an intermediate channel separation defined below full channel separation and above zero channel separation thereby to provide blended stereophonic/monophonic operation for reducing the discernible audio distortion resulting from the sudden shift toward full monophonic operation from full stereophonic operation.

Claim 4

In an FM-stereo decoder for demodulating a standard composite stereophonic signal including an L + R signal, an L - R modulated 38 KHz suppressed subcarrier signal, and a 19 KHz pilot signal; the combination comprising: means including a phase-lock-loop for generating a 38 KHz demodulating signal in phase synchronization with the 19 KHz pilot signal, the phase-lock-loop including a phase detector for producing an error voltage having an amplitude defined as a function of the phase difference between the 19 KHz pilot signal and the 38 KHz demodulating signal such that the amplitude of the error signal increases in response to shifts in the phase of the 19 KHz pilot signal Caused by distorted reception; means including an audio decoder having L and R output channels for demodulating the L + R signal and the L - R modulated 38 KHz suppressed subcarrier signal in response to the 38 KHz demodulating signal to provide an L audio signal on the L output channel and an R audio signal on the R output channel; a coupling network including an electronic switch connected across the L and R output channels of the audio decoder for establishing the separation between the L and R output channels at substantially full channel separation when the electronic switch is turned off and for establishing the separation between the L and R output channels at less than full channel separation when the electronic switch is turned on; and a level detector responsive to an initial predetermined increase in the amplitude of the error voltage due to the initiation of distorted reception to substantially instantaneously turn on the electronic switch thereby to rapidly shift toward full monophonic operation for reducing discernible audio distortion resulting from the distorted reception, the level detector including a timing network responsive to a subsequent predetermined decrease in the amplitude of the error voltage due to the termination of distorted reception to relatively gradually turn off the electronic switch thereby to slowly shift to full stereophonic operation for reducing the discernible audio disruption resulting from the shift to full stereophonic operation; the coupling network including a resistive element for establishing a minimum separation between the L and R output channels of the audio decoder when the electronic switch is turned on at an intermediate channel separation defined below full channel separation and above zero channel separation thereby to provide blended stereophonic/monophonic operation for reducing the discernible audio distortion resulting from the sudden shift toward full monophonic operation from full stereophonic operation.

Claim 5

In an FM-stereo decoder for demodulating a standard composite stereophonic signal including an L + R signal, an L - R modulated 38 KHz suppressed subcarrier signal, and a 19 KHz pilot signal; the combination comprising: means including a phase-lock-loop for generating a 38 KHz demodulating signal in phase synchronization with the 19 KHz pilot signal, the phase-lock-loop including a phase detector portion for producing an error voltage having an amplitude defined as a function of the phase difference between the 19 KHz pilot signal and the 38 KHz demodulating signal such that the amplitude of the error signal increases in response to shifts in the phase of the 19 KHz pilot signal caused by distorted reception; means including an audio decoder having L and R output channels for demodulating the L + R signal and the L - R modulated 38 KHz suppressed subcarrier signal in response to the 38 KHz demodulating signal to provide an L audio signal on the L output channel and an R audio signal on the R output channel; a coupling network including an electronic switch connected across the L and R output channels of the audio decoder for establishing substantially full channel separation when the electronic switch is turned off thereby to provide full stereophonic operation and for establishing less than full channel separation when the electronic switch is turned on thereby to provide less than full stereophonic operation; and a level detector responsive to an initial predetermined increase in the amplitude of the error voltage due to the initiation of distorted reception to substantially instantaneously turn on the electronic switch thereby to rapidly shift toward full monophonic operation for reducing the audio distortion resulting from the distorted reception, the level detector including a timing network responsive to a subsequent predeterminEd decrease in the amplitude of the error voltage due to the termination of distorted reception to relatively gradually turn off the electronic switch thereby to slowly shift to full stereophonic operation for reducing the audio disruption resulting from the shift to full stereophonic operation; the coupling network further including a reactive element for varying the separation between the L and R output channels of the audio decoder from full channel separation to less than full channel separation as a direct function of the frequency of the L and R audio signals thereby to provide blended stereophonic/monophonic operation for maximizing the stereophonic reproduction of the lower frequencies of the L and R audio signals while minimizing the audio distortion resulting from the higher frequencies of the L and R audio signals.

Claim 6

In an FM-stereo decoder for demodulating a standard composite stereophonic signal including an L + R signal, an L - R modulated 38 KHz suppressed subcarrier signal, and a 19 KHz pilot signal; the combination comprising: means including a phase-lock-loop for generating a 38 KHz demodulating signal in phase synchronization with the 19 KHz pilot signal, the phase-lock-loop including a phase detector portion for producing an error voltage having an amplitude defined as a function of the phase difference between the 19 KHz pilot signal and the 38 KHz demodulating signal such that the amplitude of the error signal increases in response to shifts in the phase of the 19 KHz pilot signal caused by distorted reception; means including an audio decoder having L and R output channels for demodulating the L + R signal and the L - R modulated 38 KHz suppressed subcarrier signal in response to the 38 KHz demodulating signal to provide an L audio signal on the L output channel and an R audio signal on the R output channel; a coupling network including an electronic switch connected across the L and R output channels of the audio decoder for establishing substantially full channel separation when the electronic switch is turned off thereby to provide full stereophonic operation and for establishing less than full channel separation when the electronic switch is turned on thereby to provide less than full stereophonic operation; and a level detector responsive to an initial predetermined increase in the amplitude of the error voltage due to the initiation of distorted reception to substantially instantaneously turn on the electronic switch thereby to rapidly shift toward full monophonic operation for reducing the audio distortion resulting from the distorted reception, the level detector including a timing network responsive to a subsequent predeterminEd decrease in the amplitude of the error voltage due to the termination of distorted reception to relatively gradually turn off the electronic switch thereby to slowly shift to full stereophonic operation for reducing the audio disruption resulting from the shift to full stereophonic operation; the coupling network further including a reactive element for varying the separation between the L and R output channels of the audio decoder from full channel separation to less than full channel separation as a direct function of the frequency of the L and R audio signals thereby to provide blended stereophonic/monophonic operation for maximizing the stereophonic reproduction of the lower frequencies of the L and R audio signals while minimizing the audio distortion resulting from the higher frequencies of the L and R audio signals.

Claim 7

In an FM-stereo decoder for demodulating a standard composite stereophonic signal including an L + R signal, an L - R modulated 38 KHz suppressed subcarrier signal, and a 19 KHz pilot signal; the combination comprising: means including a phase-lock-loop for generating a 38 KHz demodulating signal in phase synchronization with the 19 KHz pilot signal, the phase-lock-loop including a phase detector for producing an error voltage having an amplitude defined as a function of the phase difference between the 19 KHz pilot signal and the 38 KHz demodulating signal such that the amplitude of the error signal increases in response to shifts in the phase of the 19 KHz pilot signal caused by distorted reception; means including an audio decoder having L and R output channels for demodulating the L + R signal and the L - R modulated 38 KHz suppressed subcarrier signal in response to the 38 KHz demodulating signal to provide an L audio signal on the L output channel and an R audio signal on the R output channel; a coupling network including an electronic switch and at least one resistive element connected across the L and R output channels of the audio decoder for establishing full channel separation when the electronic switch is turned off thereby to provide full stereophonic operation and for establishing less than full channel separation when the electronic switch is turned on thereby to provide less than full stereophonic operation; and a level detector responsive to an initial predetermined increase in the amplitude of the error voltage due to the initiation of distorted reception to substantially instantaneously turn on the electronic switch thereby to rapidly shift toward full monophonic operation for reducing the audio distortion resulting from the distorted reception, the level detector including a timing network responsive to a subsequent predetermined decrease in the amplitude of the error voltage due to the termination of distorted reception to relatively gradually turn off the electronic switch thereby to slowly shift to full stereophonic operation for reducing audio disruption resulting from the shift to full stereophonic operation; the coupling network including a resistive element for establishing a minimum separation between the L and R output channels of the audio decoder when the electronic switch is turned on at an intermediate channel separation defined below ful channel separation and above zero channel separation by the resistance of the resistive element thereby to provide blended stereophonic/monophonic operation for reducing the audio distortion resulting from the sudden shift toward full monophonic operation, the coupling network also including a capacitive element for varying the separation between the L and R output channels of the audio decoder when the electronic switch is turned on from full channel separation to the intermediate channel separation as determined by the reactance of the capacitor thereby to provide blended stereophonic/monophonic operation for maximizing stereophonic operation at the lower frequencies of the L and R audio signals and for maximizing monophonic operation at the higher frequencies of the L and R audio signals so as to maximize the total stereophonic effect and minimize the overall audio distortion.

Claim 8

In an FM-stereo decoder for demodulating a standard composite stereophonic signal including an L + R signal, an L - R modulated 38 KHz suppressed subcarrier signal, and a 19 KHz pilot signal; the combination comprising: means including a phase-lock-loop for generating a 38 KHz demodulating signal in phase synchronization with the 19 KHz pilot signal, the phase-lock-loop including a phase detector for producing an error voltage having an amplitude defined as a function of the phase difference between the 19 KHz pilot signal and the 38 KHz demodulating signal such that the amplitude of the error signal increases in response to shifts in the phase of the 19 KHz pilot signal caused by distorted reception; means including an audio decoder having L and R output channels for demodulating the L + R signal and the L - R modulated 38 KHz suppressed subcarrier signal in response to the 38 KHz demodulating signal to provide an L audio signal on the L output channel and an R audio signal on the R output channel; a coupling network including an electronic switch and at least one resistive element connected across the L and R output channels of the audio decoder for establishing full channel separation when the electronic switch is turned off thereby to provide full stereophonic operation and for establishing less than full channel separation when the electronic switch is turned on thereby to provide less than full stereophonic operation; and a level detector responsive to an initial predetermined increase in the amplitude of the error voltage due to the initiation of distorted reception to substantially instantaneously turn on the electronic switch thereby to rapidly shift toward full monophonic operation for reducing the audio distortion resulting from the distorted reception, the level detector including a timing network responsive to a subsequent predetermined decrease in the amplitude of the error voltage due to the termination of distorted reception to relatively gradually turn off the electronic switch thereby to slowly shift to full stereophonic operation for reducing audio disruption resulting from the shift to full stereophonic operation; the coupling network including a resistive element for establishing a minimum separation between the L and R output channels of the audio decoder when the electronic switch is turned on at an intermediate channel separation defined below ful channel separation and above zero channel separation by the resistance of the resistive element thereby to provide blended stereophonic/monophonic operation for reducing the audio distortion resulting from the sudden shift toward full monophonic operation, the coupling network also including a capacitive element for varying the separation between the L and R output channels of the audio decoder when the electronic switch is turned on from full channel separation to the intermediate channel separation as determined by the reactance of the capacitor thereby to provide blended stereophonic/monophonic operation for maximizing stereophonic operation at the lower frequencies of the L and R audio signals and for maximizing monophonic operation at the higher frequencies of the L and R audio signals so as to maximize the total stereophonic effect and minimize the overall audio distortion.