Compatible transmission techniques for FM stereophonic radio and television

Claim 3

Method according to claim 1, wherein said step of combining and expanding comprises the steps of: separately demodulating the received difference and compressed difference signals S and S', summing said demodulated signals S and S' to obtain the sum signal (S+S'), and expanding said sum signal to obtain said noise-reduced difference signal.

Claim 4

Method according to claim 1, wherein said step of combining and expanding comprises the steps of: quadrature demodulating the received difference and compressed difference signals S and S' and producing an output signal representing the square root of the sum of the squares of the signals S and S', and expanding said output signal to obtain said noise-reduced difference signal.

Claim 5

Method according to claim 1 in which the step of transmitting includes the step of compressing said difference signal in accordance with an infinity-to-one characteristic having a slope of one for input signal levels below a predetermined level and a slope substantially equal to infinity for input signal levels greater than said predetermined level.

Claim 6

Method according to claim 1 in which the step of transmitting includes the step of compressing said difference signal in accordnace with a re-entrant characteristic having unity slope for input signal levels below a first predetermined level, and a slope slightly less then infinity for input signal signal levels greater then said first predetermined level and less then a second higher predetermined level.

Claim 7

Method according to claim 1 wherein the step of transmitting includes the steps of amplitude-modulating first and second sub-carrier signals with said difference signal S and with said compressed difference signal S', respectively, and modulating said sum signal M and the said modulated sub-carrier signals onto a high frequency carrier for the purpose of transmitting the same.

Claim 8

Method according to claim 6 wherein said first and second sub-carrier signals have the same frequency and are displaced relative to each other by 90°.

Claim 9

A receiver for use in a biphonic FM radio transmission system including a transmitter having means for combining two independent stereophonically related audio frequency signals L and R to obtain sum and difference signals M and S respectively comprising (L+R) and (L-R), means for compressing the dynamic range of said difference signal S and producing a compressed difference signal S', means for modulating each of two sub-carriers with a respective one of said difference and compressed difference signals S and S', and means for frequency modulating the aforementioned modulated sub-carrier signals and said sum signal M onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers, said receiver comprising: demultiplexing means for deriving said sum signal M, said difference signal S and said compressed difference signal S', means for combining the derived difference signal S with the derived compressed difference signal S' and for expanding the combined signal to obtain a noise-reduced difference signal having an amplitude level substantially equal to that of the derived difference signal S, and de-matrix means for combining said noise-reduced difference signal with said sum signal M to obtain said left (L) and (R) channel stereophonic signals.

Claim 10

A receiver for use in a biphonic FM radio transmission system including a transmitter having means for combining two independent stereophonically related audio frequency signals L and R to obtain sum and difference signals M and S respectively comprising (L+R) and (L-R), means for compressing the dynamic range of said difference signal S and producing a compressed difference signal S', means for modulating each of two sub-carriers with a respective one of said difference and compressed difference signals S and S', and means for frequency modulating the aforementioned modulated sub-carrier signals and said sum signal M onto a high frequency carrier for the purpose of transmitting the same to one or more remote receivers, said receiver comprising: demultiplexing means for deriving said sum signal M, said difference signal S and said compressed difference signal S', means for combining the derived difference signal S with the derived compressed difference signal S' and for expanding the combined signal to obtain a noise-reduced difference signal having an amplitude level substantially equal to that of the derived difference signal S, and de-matrix means for combining said noise-reduced difference signal with said sum signal M to obtain said left (L) and (R) channel stereophonic signals.

Claim 11

A receiver as defined by claim 8 for use with a transmitter in which said sub-carriers are of the same frequency and displaced in phase by 90° and wherein said means for combining and expanding comprises: first and second demodulators for separately demodulating the received sub-carrier signals respectively amplitude-modulated by said difference and compressed difference signals S and S' for obtaining said signals S and S', means connected to receive and for summing said signals S and S' to obtain the sum signal (S+S'), and expander means for expanding said sum signal (S+S') to obtain said noise-reduced difference signal.

Claim 12

A receiver as defined by claim 8 for use with a transmitter in which the two sub-carriers have the same frequency and are displaced in phase by 90° and respectively amplitude-modulated by said difference signal S and said compressed difference signal S', wherein said combining and expanding means comprises a quadrature demodulator having a single demodulating axis position at 45° with respect to each of said sub-carriers for demodulating the received amplitude-modulated quadrature-related sub-carriers and producing an output signal representing the square root of the sum of the squares of the difference signal S and the compressed difference signal S', and means for expanding said output signal to obtain said noise-reduced difference signal.

Claim 13

A receiver as defined in claim 9, wherein said receiver further comprises: switch means connected to said de-matrix means and operative alternatively to couple the difference signal S obtained from said first demodulator, instead of the noise-reduced difference signal, to said de-matrix means for enabling said receiver for reproducing conventional two-channel stereophonic broadcasts.

Claim 14

An improved biphonic FM radio transmission system for transmitting independent stereophonically related left and right channel signals, said system comprising: at the transmitter matrix means for combining the left and right channel stereophonic signals to obtain a sum signal M corresponding to the sum of the left and right channel signals and a difference signal S corresponding to the difference between the left and right channel signals; compressor means connected to said matrix means for compressing the dynamic range of said difference signal S to produce a compressed difference signal S' which is compressed according to a desired compression law; generating means for generating two sub-carriers of the same frequency and spaced 90° apart in phase and a pilot signal having a frequency which is one-half the frequency of the sub-carriers; amplitude-modulating means connected to said generating means, said compressor means and said matrix means for amplitude-modulating each sub-carrier with a respective one of said difference and compressed difference signals S and S' to develop two double-sideband suppressed-carrier signals, the frequency of said sub-carriers being sufficiently high as to insure a frequency gap between the lower sidebands of the modulated sub-carrier signals and the frequency bandwidth of said sum signal M, with the frequency of the pilot signal being located within said gap; and frequency modulating means connected for frequency modulating the modulated sub-carrier signals, the pilot signal, and the sum signal M onto a high-frequency carrier for the purpose of transmitting the same to one or more remote receivers; and at the receiver deriving means for receiving said frequency modulated high-frequency carrier and for deriving said sum signal M and said amplitude-modulated sub-carriers respectively modulated by said difference signal S and said compressed difference signal S'; means including demodulator means for combining and demodulating the amplitude-modulated sub-carrier signals for producing a combined signal and for expanding the combined signal to obtain a noise-reduced difference signal having an amplitude level substantially equal to that of the received difference signal; and de-matrix means connected to receive and for combining said noise-reduced difference signal with said sum signal M to obtain said left and right channel stereophonic signals.

Claim 15

An improved biphonic FM radio transmission system for transmitting independent stereophonically related left and right channel signals, said system comprising: at the transmitter matrix means for combining the left and right channel stereophonic signals to obtain a sum signal M corresponding to the sum of the left and right channel signals and a difference signal S corresponding to the difference between the left and right channel signals; compressor means connected to said matrix means for compressing the dynamic range of said difference signal S to produce a compressed difference signal S' which is compressed according to a desired compression law; generating means for generating two sub-carriers of the same frequency and spaced 90° apart in phase and a pilot signal having a frequency which is one-half the frequency of the sub-carriers; amplitude-modulating means connected to said generating means, said compressor means and said matrix means for amplitude-modulating each sub-carrier with a respective one of said difference and compressed difference signals S and S' to develop two double-sideband suppressed-carrier signals, the frequency of said sub-carriers being sufficiently high as to insure a frequency gap between the lower sidebands of the modulated sub-carrier signals and the frequency bandwidth of said sum signal M, with the frequency of the pilot signal being located within said gap; and frequency modulating means connected for frequency modulating the modulated sub-carrier signals, the pilot signal, and the sum signal M onto a high-frequency carrier for the purpose of transmitting the same to one or more remote receivers; and at the receiver deriving means for receiving said frequency modulated high-frequency carrier and for deriving said sum signal M and said amplitude-modulated sub-carriers respectively modulated by said difference signal S and said compressed difference signal S'; means including demodulator means for combining and demodulating the amplitude-modulated sub-carrier signals for producing a combined signal and for expanding the combined signal to obtain a noise-reduced difference signal having an amplitude level substantially equal to that of the received difference signal; and de-matrix means connected to receive and for combining said noise-reduced difference signal with said sum signal M to obtain said left and right channel stereophonic signals.

Claim 16

A biphonic FM radio transmission system as defined in claim 12, wherein said demodulator means comprises first and second demodulators each for demodulating a different one of said amplitude-modulated sub-carriers to derive said difference signal S and said compressed difference signal S', wherein said combining means includes means for summing said difference signal S and said compressed difference signal S' to produce a sum signal (S+S'), and wherein said means for expanding comprises an expander for expanding said sum signal (S+S') to obtain said noise-reduced difference signal.

Claim 17

A biphonic FM radio transmission system as defined in claim 13, wherein said receiver further comprises: switch means connected to said de-matrix means and operative alternatively to couple the difference signal S produced by said first demodulator, instead of the noise-reduced difference signal, to the de-matrix means for enabling said receiver for reproducing conventional two-channel stereophonic broadcasts.

Claim 18

A biphonic FM radio transmission system as defined in claim 12 wherein said demodulator means comprises a quadrature demodulator having a demodulation axis positioned at 45° from the axes of the two sub-carriers and connected to receive said amplitude-modulated sub-carriers for producing an output signal representing the square root of the sum of the squares of the difference signal S and the compressed difference signal S' and wherein said means for expanding comprises and expander connected to receive and for expanding said output signal to obtain said noise-reduced difference signal.

Claim 19

A biphonic FM radio transmission system as defined in claim 12, wherein the compressor in the transmitter has a compression characteristic which has unity slope for input signal levels up to a predetermined input signal level and which has infinity slope for input signal levels above said predetermined level.

Claim 20

A biphonic FM radio transmission system as defined in claim 12, wherein the compressor in the transmitter has a compression characteristic which has unity slope for input signal levels below a first predetermined level, and a slightly negative slope for input signal levels greater than said first predetermined level and less than a second higher predetermined level.