Compatible four channel fm system

Claim 2

In a four channel broadcasting system, a method for providing a compatible four channel composite signal for use in conjunction with an FM radio transmitter having said composite signal modulated on the carrier thereof and consisting of a main channel, a synchronizing pilot signal of a first predetermined frequency, a first sub-channel centered at the second harmonic of said pilot signal and a second sub-channel centered at the fourth harmonic of said pilot signal comprising the steps of: providing first, second, third and fourth audio signals; providing a pilot signal of a first predetermined frequency; providing a first subcarrier frequency signal at twice the frequency of said pilot signal; providing a second sub-carrier frequency signal at quadruple the frequency of said pilot signal; applying said first and second audio signals to a first audio gate and switching said first gate at the frequency of said second sub-carrier frequency signal; applying said third and fourth audio signals to a second audio gate and switching said second audio gate at the frequency of said second subcarrier frequency signal; applying the outputs from said first and second audio gates to a third audio gate and switching said third audio gate at the frequency of said first sub-carrier frequency signal; and combining the output of said third audio gate with said pilot to obtain said composite signal.

Claim 3

In a four channel receiving system, a method for decoding first, second, third and fourth audio signals from a compatible four channel composite signal adapted to be received from an FM radio transmitter having said composite signal modulated on the carrier thereof, said composite signal consisting of a main channel, a synchronizing pilot signal of a first predetermined frequency, a first sub-channel centered at the second harmonic of said pilot signal and a second sub-channel centered at the fourth harmonic of said pilot signal, comprising the steps of: extracting said pilot signal; providing a first switching signal at twice the frequency of said pilot signal; providing a second switching signal at quadruple the frequency of said pilot signal; applying said composite signal to a first audio gate and switching said first audio gate at a frequency equal to the frequency of said first switching signal to provide a first gate output signal and a second gate output signal; applying said first gate output signal to a second audio gate and switching said second audio gate at a frequency equal to the frequency of said second switching signal to provide said first and second audio signals; and applying said second gate output signal to a third audio gate and switching said third audio gate at a frequency equal to the frequency of said second switching signal to provide said third and fourth audio signals.

Claim 4

In a four channel receiving system, a method for decoding first, second, third and fourth audio signals from a compatible four channel composite signal adapted to be received from an FM radio transmitter having said composite signal modulated on the carrier thereof, said composite signal consisting of a main channel, a synchronizing pilot signal of a first predetermined frequency, a first sub-channel centered at the second harmonic of said pilot signal and a second sub-channel centered at the fourth harmonic of said pilot signal, comprising the steps of: extracting said pilot signal; providing a first switching signal at twice the frequency of said pilot signal; providing a second switching signal at quadruple the frequency of said pilot signal; applying said composite signal to a first audio gate and switching said first audio gate at a frequency equal to the frequency of said first switching signal to provide a first gate output signal and a second gate output signal; applying said first gate output signal to a second audio gate and switching said second audio gate at a frequency equal to the frequency of said second switching signal to provide said first and second audio signals; and applying said second gate output signal to a third audio gate and switching said third audio gate at a frequency equal to the frequency of said second switching signal to provide said third and fourth audio signals.

Claim 5

In a four channel broadcasting system, a method for providing a compatible four channel composite signal for use in conjunction with an FM radio transmitter for transmitting said composite signal, which composite signal includes a main channel with first, plus second, plus third and plus fourth audio signals combined thereon, a pilot signal of a predetermined frequency removed from said main channel, a first suppressed sub-channel centered on a frequency equal to the second harmonic of said pilot signal, said first sub-channel having first, plus second, minus third, minus fourth audio signals and in quadrautre therewith first, minus second, minus third and plus fourth audio signals combined thereon and a second suppressed sub-channel centered on a frequency twice that of said first sub-channel having first, minus second, plus third, minus fourth audio signals combined thereon, comprising the steps of: providing a pilot signal of a first predetermined frequency; providing a first switching signal at twice the frequency of said pilot signal; providing a second switching signal at quadruple the frequency of said pilot signal; utilizing said second switching signal to switch between said first and second audio signals to obtain a first signal; utilizing said second switching signal to switch between said third and fourth audio signals to obtain a second signal; utilizing said first switching signal to switch between said first and second signals to obtain a third signal; combining said third signal with said pilot signal to obtain said composite signal; and modulating said FM transmitter with said composite signal.

Claim 6

In a four channel broadcasting system, a method for providing a compatible four channel composite signal for use in conjunction with an FM radio transmitter for transmitting said composite signal, which composite signal includes a main channel with first, plus second, plus third and plus fourth audio signals combined thereon, a pilot signal of a predetermined frequency removed from said main channel, a first suppressed sub-channel centered on a frequency equal to the second harmonic of said pilot signal, said first sub-channel having first, plus second, minus third, minus fourth audio signals and in quadrautre therewith first, minus second, minus third and plus fourth audio signals combined thereon and a second suppressed sub-channel centered on a frequency twice that of said first sub-channel having first, minus second, plus third, minus fourth audio signals combined thereon, comprising the steps of: providing a pilot signal of a first predetermined frequency; providing a first switching signal at twice the frequency of said pilot signal; providing a second switching signal at quadruple the frequency of said pilot signal; utilizing said second switching signal to switch between said first and second audio signals to obtain a first signal; utilizing said second switching signal to switch between said third and fourth audio signals to obtain a second signal; utilizing said first switching signal to switch between said first and second signals to obtain a third signal; combining said third signal with said pilot signal to obtain said composite signal; and modulating said FM transmitter with said composite signal.

Claim 7

The method according to claim 3 further comprising the steps of: providing a main channel extending up to a frequency less than the frequency of said pilot signal and having first, plus second, plus third, plus fourth audio signals combined thereon; providing a suppressed sub-channel centered at twice the frequency of said pilot signal and having first, plus second, minus third, minus fourth audio signals and in quadrature therewith first, minus second, minus third and plus fourth audio signals combined thereon; and providing a second suppressed sub-channel at quadruple the frequency of said pilot signal and having first, minus second, plus third, minus fourth audio signals combined thereon.

Claim 8

In a four channel receiving system, a method for deriving first, second, third and fourth audio signals from a compatible four channel composite signal received from an FM radio transmitter, which composite signal includes a main channel with first, plus second, plus third and plus fourth audio signals combined thereon, a pilot signal having a predetermined frequency removed from said main channel, a first suppressed sub-channel which is centered at the second harmonic of said pilot signal, said first sub-channel having first, plus second, minus third, minus fourth audio signals and in quadrature therewith first, minus second, minus third and plus fourth audio signals combined thereon and a second suppressed sub-channel centered at the fourth harmonic of said pilot signal and having first, minus second, plus third, minus fourth audio signals combined thereon comprising the steps of: deriving a signal equal in frequency to the frequency of said pilot signal; deriving a first switching signal equal in frequency to twice the frequency of said pilot signal; deriving a second switching signal equal in frequency to quadruple the frequency of said pilot signal; utilizing said first switching signal to switch said composite sigNal at twice the frequency of said pilot signal to obtain a first signal and a second signal; utilizing said second switching signal to switch said first signal at quadruple the frequency of said pilot signal to obtain said first and second audio signals; and utilizing said second switching signal to switch said second signal at quadruple the frequency of said pilot signal to obtain said third and fourth audio signals.

Claim 9

In a four channel receiving system, a method for deriving first, second, third and fourth audio signals from a compatible four channel composite signal received from an FM radio transmitter, which composite signal includes a main channel with first, plus second, plus third and plus fourth audio signals combined thereon, a pilot signal having a predetermined frequency removed from said main channel, a first suppressed sub-channel which is centered at the second harmonic of said pilot signal, said first sub-channel having first, plus second, minus third, minus fourth audio signals and in quadrature therewith first, minus second, minus third and plus fourth audio signals combined thereon and a second suppressed sub-channel centered at the fourth harmonic of said pilot signal and having first, minus second, plus third, minus fourth audio signals combined thereon comprising the steps of: deriving a signal equal in frequency to the frequency of said pilot signal; deriving a first switching signal equal in frequency to twice the frequency of said pilot signal; deriving a second switching signal equal in frequency to quadruple the frequency of said pilot signal; utilizing said first switching signal to switch said composite sigNal at twice the frequency of said pilot signal to obtain a first signal and a second signal; utilizing said second switching signal to switch said first signal at quadruple the frequency of said pilot signal to obtain said first and second audio signals; and utilizing said second switching signal to switch said second signal at quadruple the frequency of said pilot signal to obtain said third and fourth audio signals.

Claim 10

In a four channel broadcasting system, a method for providing a four channel composite signal compatible with existing mono and stereo standards for use in conjunction with an FM radio transmitter having a predetermined carrier frequency, comprising the steps of: providing a main channel extending up to a first predetermined frequency and having first, plus second, plus third and plus fourth audio signals combined thereon; providing a pilot signal of a second predetermined frequency removed from said carrier frequency; providing a first sub-channel centered at the second harmonic of the frequency of said pilot signal and containing two sub-carriers; modulating the first sub-carrier of said first sub-channel with the plus first, plus second, minus third, minus fourth audio signals and modulating in quadrature therewith the second sub-carrier of said first sub-channel with plus first, minus second, minus third and plus fourth audio signals; providing a second sub-channel centered at the fourth harmonic of the frequency of said pilot signal and containing a sub-carrier; and modulating the sub-carrier of said second sub-channel with the plus first, minus second, plus third and minus fourth audio signals.

Claim 11

In a four channel broadcasting system, a method for providing a four channel composite signal compatible with existing mono and stereo standards for use in conjunction with an FM radio transmitter having a predetermined carrier frequency, comprising the steps of: providing a main channel extending up to a first predetermined frequency and having first, plus second, plus third and plus fourth audio signals combined thereon; providing a pilot signal of a second predetermined frequency removed from said carrier frequency; providing a first sub-channel centered at the second harmonic of the frequency of said pilot signal and containing two sub-carriers; modulating the first sub-carrier of said first sub-channel with the plus first, plus second, minus third, minus fourth audio signals and modulating in quadrature therewith the second sub-carrier of said first sub-channel with plus first, minus second, minus third and plus fourth audio signals; providing a second sub-channel centered at the fourth harmonic of the frequency of said pilot signal and containing a sub-carrier; and modulating the sub-carrier of said second sub-channel with the plus first, minus second, plus third and minus fourth audio signals.

Claim 12

In a four channel broadcasting system, a system for providing a compatible four channel composite signal for use in conjunction with an FM radio transmitter having said composite signal modulated on the carrier thereof and consisting of a main channel, synchronizing pilot signal of a first predetermined frequency, a first sub-channel centered at the second harmonic of said pilot signal and a second sub-channel centered at the fourth harmonic of said pilot signal comprising: means for providing first, second, third and fourth audio signals; means for providing a pilot signal of a first predetermined frequency; means for providing a first sub-carrier frequency signal at twice the frequency of said pilot signal; means for providing a second sub-carrier frequency signal at quadruple the frequency of said pilot signal; a first audio gate; means for applying said first and second audio signals to said first audio gate; means for switching said first audio gate at the frequency of said second sub-carrier frequency signal; a second audio gate; means for applying said third and fourth audio signals to said second audio gate; means for switching said second audio gate at the frequency of said second sub-carrier frequency signal; a third audio gate; means for applying the outputs from said first and second audio gates to said third audio gate; means for switching said third audio gate at the frequency of said first sub-carrier frequency signal; and means for combining the output of said third audio gate with said pilot signal to obtain said composite signal.

Claim 13

In a four channel broadcasting system, a system for providing a compatible four channel composite signal for use in conjunction with an FM radio transmitter having said composite signal modulated on the carrier thereof and consisting of a main channel, synchronizing pilot signal of a first predetermined frequency, a first sub-channel centered at the second harmonic of said pilot signal and a second sub-channel centered at the fourth harmonic of said pilot signal comprising: means for providing first, second, third and fourth audio signals; means for providing a pilot signal of a first predetermined frequency; means for providing a first sub-carrier frequency signal at twice the frequency of said pilot signal; means for providing a second sub-carrier frequency signal at quadruple the frequency of said pilot signal; a first audio gate; means for applying said first and second audio signals to said first audio gate; means for switching said first audio gate at the frequency of said second sub-carrier frequency signal; a second audio gate; means for applying said third and fourth audio signals to said second audio gate; means for switching said second audio gate at the frequency of said second sub-carrier frequency signal; a third audio gate; means for applying the outputs from said first and second audio gates to said third audio gate; means for switching said third audio gate at the frequency of said first sub-carrier frequency signal; and means for combining the output of said third audio gate with said pilot signal to obtain said composite signal.

Claim 14

In a four channel receiving system, a system for decoding first, second, third and fourth audio signals from a compatible four channel composite signal adapted to be received from an FM radio transistor having said composite signal modulated on the carrier thereof, said composite signal consisting of a main channel, a synchronizing pilot signal of a first predetermined frequency, a first sub-channel centered at the second harmonic of said pilot signal and a second sub-channel centered at the fourth harmonic of said pilot signal, comprising: means for extracting said pilot signal from said composite signal; means for providing a first switching signal at twice the frequency of said pilot signal; means for providing a second switching signal at quadruple the frequency of said pilot signal; a first audio gaTe; means for applying said composite signal to said first audio gate; means for switching said first audio gate at a frequency equal to the frequency of said first switching signal to provide a first gate output signal and a second gate output signal; a second audio gate; means for applying said first gate output signal to said second audio gate; means for switching said second audio gate at a frequency equal to the frequency of said second switching signal to provide said first and second audio signals; a third audio gate; means for applying said second gate output signal to said third audio gate; and means for switching said third audio gate at a frequency equal to the frequency of said second switching signal to provide said third and fourth audio signals.

Claim 15

In a four channel receiving system, a system for decoding first, second, third and fourth audio signals from a compatible four channel composite signal adapted to be received from an FM radio transistor having said composite signal modulated on the carrier thereof, said composite signal consisting of a main channel, a synchronizing pilot signal of a first predetermined frequency, a first sub-channel centered at the second harmonic of said pilot signal and a second sub-channel centered at the fourth harmonic of said pilot signal, comprising: means for extracting said pilot signal from said composite signal; means for providing a first switching signal at twice the frequency of said pilot signal; means for providing a second switching signal at quadruple the frequency of said pilot signal; a first audio gaTe; means for applying said composite signal to said first audio gate; means for switching said first audio gate at a frequency equal to the frequency of said first switching signal to provide a first gate output signal and a second gate output signal; a second audio gate; means for applying said first gate output signal to said second audio gate; means for switching said second audio gate at a frequency equal to the frequency of said second switching signal to provide said first and second audio signals; a third audio gate; means for applying said second gate output signal to said third audio gate; and means for switching said third audio gate at a frequency equal to the frequency of said second switching signal to provide said third and fourth audio signals.

Claim 16

In a four channel broadcasting system, a system for providing a compatible four channel composite signal for use in conjunction with an FM radio transmitter for transmitting said composite signal, which composite signal includes a main channel with first, plus second, plus third and plus fourth audio signals combined thereon, a pilot signal of a predetermined frequency removed from said main channel, a first suppressed subchannel centerd on a frequency equal to the second harmonic of said pilot signal, said first sub-channel having first, plus second, minus third, minus fourth audio signals and in quadrature therewith first, minus second, minus third and plus fourth audio signals combined thereon and a second suppressed sub-channel centered on a frequency twice that of said first sub-channel having first, minus second, plus third, minus fourth audio signals combined thereon, comprising: means for providing a pilot signal of a first predetermined frequency; means for providing a first switching signal at twice the frequency of said pilot signal; means for providing a second switching signal at quadruple the frequency of said pilot signal; means for switching between said first and second audio signals at quadruple the frequency of said pilot signal to obtain a first signal; means for switching between said third and fourth audio signals at quadruple the frequency of said pilot signal to obtain a second signal; means for switching between said first and third signals at twice the frequency of said pilot signal to obtain a third signal; and means for combining said third signal with said pilot signal to obtain said composite signal.

Claim 17

In a four channel broadcasting system, a system for providing a compatible four channel composite signal for use in conjunction with an FM radio transmitter for transmitting said composite signal, which composite signal includes a main channel with first, plus second, plus third and plus fourth audio signals combined thereon, a pilot signal of a predetermined frequency removed from said main channel, a first suppressed subchannel centerd on a frequency equal to the second harmonic of said pilot signal, said first sub-channel having first, plus second, minus third, minus fourth audio signals and in quadrature therewith first, minus second, minus third and plus fourth audio signals combined thereon and a second suppressed sub-channel centered on a frequency twice that of said first sub-channel having first, minus second, plus third, minus fourth audio signals combined thereon, comprising: means for providing a pilot signal of a first predetermined frequency; means for providing a first switching signal at twice the frequency of said pilot signal; means for providing a second switching signal at quadruple the frequency of said pilot signal; means for switching between said first and second audio signals at quadruple the frequency of said pilot signal to obtain a first signal; means for switching between said third and fourth audio signals at quadruple the frequency of said pilot signal to obtain a second signal; means for switching between said first and third signals at twice the frequency of said pilot signal to obtain a third signal; and means for combining said third signal with said pilot signal to obtain said composite signal.

Claim 18

The system according to claim 9 wherein said composite signal includes a main channel extending up to a frequency less than the frequency of said pilot signal and having first, plus second, plus third, plus fourth audio signal combined thereon; a suppressed sub-channel centered at twice the frequency of said pilot signal and having first, plus second, minus third, minus fourth audio signals and in quadrature therewith first, minus second, minus third and plus fourth audio signals combined thereon; and a second suppressed sub-channel at quadruple the frequency of said pilot signal and having first, minus second, plus third, minus fourth audio signals combined thereon.

Claim 19

In a four channel receiving system, a system for deriving first, second, third and fourth audio signals from a compatible four channel composite signal received from an FM radio transmitter, which composite signal includes a main channel with first, plus second, plus third and plus fourth audio signals combined thereon, a pilot signal having a predetermined frequency removed from said main channel, a first suppressed sub-channel which is centered at the second harmonic of said pilot signal, said first sub-channel having first, plus second, minus third, minus fourth audio signals and in quadrature therewith first, minus second, minus third and plus fourth audio signals combined thereon and a second suppressed sub-channel centered at the fourth harmonic of said pilot signal and having first, minus second, plus third, minus fourth audio signals combined thereon comprising: means for deriving a signal equal in Frequency to the frequency of said pilot signal; means for deriving a first switching signal equal in frequency to twice the frequency of said pilot signal; means for deriving a second switching signal equal in frequency to quadruple the frequency of said pilot signal; means for utilizing said first switching signal to switch said composite signal at twice the frequency of said pilot signal to obtain a first signal and a second signal; means for utilizing said second switching signal to switch said first signal at quadruple the frequency of said pilot signal to obtain said first and second audio signals; and means for utilizing said second switching signal to switch said second signal at quadruple the frequency of said pilot signal to obtain said third and fourth audio signals.

Claim 20

In a four channel receiving system, a system for deriving first, second, third and fourth audio signals from a compatible four channel composite signal received from an FM radio transmitter, which composite signal includes a main channel with first, plus second, plus third and plus fourth audio signals combined thereon, a pilot signal having a predetermined frequency removed from said main channel, a first suppressed sub-channel which is centered at the second harmonic of said pilot signal, said first sub-channel having first, plus second, minus third, minus fourth audio signals and in quadrature therewith first, minus second, minus third and plus fourth audio signals combined thereon and a second suppressed sub-channel centered at the fourth harmonic of said pilot signal and having first, minus second, plus third, minus fourth audio signals combined thereon comprising: means for deriving a signal equal in Frequency to the frequency of said pilot signal; means for deriving a first switching signal equal in frequency to twice the frequency of said pilot signal; means for deriving a second switching signal equal in frequency to quadruple the frequency of said pilot signal; means for utilizing said first switching signal to switch said composite signal at twice the frequency of said pilot signal to obtain a first signal and a second signal; means for utilizing said second switching signal to switch said first signal at quadruple the frequency of said pilot signal to obtain said first and second audio signals; and means for utilizing said second switching signal to switch said second signal at quadruple the frequency of said pilot signal to obtain said third and fourth audio signals.

Claim 21

In a four channel broadcasting system, a system for providing a four channel composite signal compatible with existing mono and stereo standards for use in conjunction with an FM radio transmitter having a predetermined carrier frequency, comprising: means for providing a main channel extending up to a first predetermined frequency and having first, plus second, plus third and plus fourth audio signals combined thereon; means for providing a pilot signal of a second predetermined frequency removed from said carrier frequency; means for providing a first sub-channel centered at the second harmonic of the frequency of said pilot signal and containing two sub-carriers; means for modulating the first sub-carrier of said first sub-channel with the plus first, plus second, minus third, minus fourth audio signals and for modulating in quadrature therewith the second sub-carrier of said first sub-channel with plus first, minus second, minus third and plus fourth audio signals; means for providing a second sub-channel centered at the fourth harmonic of the frequency of said pilot signal and containing a subcarrier; and means for modulating the sub-carrier of said second sub-channel with the plus first, minus second, plus third and minus fourth audio signals.

Claim 22

In a four channel broadcasting system, a system for providing a four channel composite signal compatible with existing mono and stereo standards for use in conjunction with an FM radio transmitter having a predetermined carrier frequency, comprising: means for providing a main channel extending up to a first predetermined frequency and having first, plus second, plus third and plus fourth audio signals combined thereon; means for providing a pilot signal of a second predetermined frequency removed from said carrier frequency; means for providing a first sub-channel centered at the second harmonic of the frequency of said pilot signal and containing two sub-carriers; means for modulating the first sub-carrier of said first sub-channel with the plus first, plus second, minus third, minus fourth audio signals and for modulating in quadrature therewith the second sub-carrier of said first sub-channel with plus first, minus second, minus third and plus fourth audio signals; means for providing a second sub-channel centered at the fourth harmonic of the frequency of said pilot signal and containing a subcarrier; and means for modulating the sub-carrier of said second sub-channel with the plus first, minus second, plus third and minus fourth audio signals.

Claim 23

A compatible four channel audio system for providing a compatible four channel composite signal comprising means for providing left front, left rear, right front and right rear audio signals, means for providing a 19 kHz pilot signal, means for providing a 38 kHz sub-carrier signal, first circuit means coupled to said left front and left rear audio signals for combining all frequencies of said left front and left rear audio signals above 4 kHz and for providing separation between said left front and left rear audio signals at frequencies less than 4 kHz, first encoder means coupled to said first circuit means and said left front and left rear audio signals, said first encoder means including first switch means responsive to said pilot signal for providing a first encoder output during the positive half cycle of said pilot signal and second switch means responsive to said pilot signal for providing a second encoder output during the negative half cycle of said pilot signal, second circuit means coupled to said right front and right rear audio signals for combining all frequencies of said right front and right rear audio signals above 4 kHz and for providing separation between said right front and right rear audio signals at frequencies less than 4 kHz, second encoder means coupled to said second circuit means and said right front and right rear audio signals, said second encoder means including first switch means responsive to said pilot signal for providing a first encoder output during the positive half cycle of said pilot signal and said second switch means responsive to said pilot signal for providing a second encoder output during the negative half cycle of said pilot signal, means for combining the output signals from said first and second encoder means to provide said composite signal, and transmitter means for transmitting said composite signal, said transmitter means responsive to said 38 kHz sub-carrier signal for transmitting for transmitting during the positive cycles of said subcarrier signal a main channel having left front plus right front audio signals modulated thereon, said 19 kHz pilot signal and a suppressed sub-channel having left front minus right front audio signals modulated thereon and for transmitting during the negative cycles of said sub-carrier signal a main channel having left rear plus right rear audio signals modulated thereon, said 19 kHz pilot signal and a suppressed sub-channel having left rear minus right rear signals modulated thereon.

Claim 24

A compatible four channel audio system for providing a compatible four channel composite signal comprising means for providing left front, left rear, right front and right rear audio signals, means for providing a 19 kHz pilot signal, means for providing a 38 kHz sub-carrier signal, first circuit means coupled to said left front and left rear audio signals for combining all frequencies of said left front and left rear audio signals above 4 kHz and for providing separation between said left front and left rear audio signals at frequencies less than 4 kHz, first encoder means coupled to said first circuit means and said left front and left rear audio signals, said first encoder means including first switch means responsive to said pilot signal for providing a first encoder output during the positive half cycle of said pilot signal and second switch means responsive to said pilot signal for providing a second encoder output during the negative half cycle of said pilot signal, second circuit means coupled to said right front and right rear audio signals for combining all frequencies of said right front and right rear audio signals above 4 kHz and for providing separation between said right front and right rear audio signals at frequencies less than 4 kHz, second encoder means coupled to said second circuit means and said right front and right rear audio signals, said second encoder means including first switch means responsive to said pilot signal for providing a first encoder output during the positive half cycle of said pilot signal and said second switch means responsive to said pilot signal for providing a second encoder output during the negative half cycle of said pilot signal, means for combining the output signals from said first and second encoder means to provide said composite signal, and transmitter means for transmitting said composite signal, said transmitter means responsive to said 38 kHz sub-carrier signal for transmitting for transmitting during the positive cycles of said subcarrier signal a main channel having left front plus right front audio signals modulated thereon, said 19 kHz pilot signal and a suppressed sub-channel having left front minus right front audio signals modulated thereon and for transmitting during the negative cycles of said sub-carrier signal a main channel having left rear plus right rear audio signals modulated thereon, said 19 kHz pilot signal and a suppressed sub-channel having left rear minus right rear signals modulated thereon.

Claim 25

The system according to claim 13 further including means for receiving said composite signal, means for extracting said 19 kHz pilot signal from said composite signal, first decoder means adapted to receive the left front and left rear audio signals, and first decoder including first switch means responsive to said pilot signal for providing said left front audio signal during the positive half cycle of said pilot signal and second switch means responsive to said pilot signal for providing said left rear audio signal during the negative half cycle of said pilot signal, and second decoder means adapted to receive said right front and right rear audio signals, said second decoder means including first switch means responsive to said pilot signal for providing said right front audio signal during the positive half cycle of said pilot signal and second switch means responsive to said pilot signal for providing said right rear audio signal during the negative half cycle of said pilot signal.