US 4,602,380 A · Compatible transmission techniques for FM stereophonic radio and television

Abstract

A stereophonic broadcasting system incorporating companding of the difference signal in which both the usual difference signal and a compressed version of the difference signal are transmitted to one or more remote receivers. At the receiver the usual difference signal and the compressed difference signal are combined and the resulting signal then expanded to obtain a noise-reduced difference signal for matrixing with the sum signal to obtain the original left and right signals. Utilizing both difference signals increases the effective level of the received difference signal by 6 dB, whereas the noise is increased only 3 dB, for a net improvement of 3 dB in signal-to-noise ratio. Utilization of both difference signals at the receiver also permits compression of the difference signal according to any desired compression law.

Claims17

Dependent claims

A method for extending the range and for increasing the channel capacity of an FM stereophonic radio broadcast system as compared to the conventional two-channel FM stereophonic system while maintaining compatibility with conventional monophonic and two-channel receivers, comprising the steps of:

transmitting sum (M) and difference (S) signals respectively corresponding to the sum of left and right channel stereophonic signals and to the difference between the left and right channel stereophonic signals, and a compressed difference signal (S') which contains substantially the same information as said difference signal (S) and is compressed according to a desired compression law,
receiving said sum signal M, said difference signal S and said compressed difference signal S',
combining the received difference signal S with the received compressed difference signal S' and expanding the combined signal to obtain a noise-reduced difference signal having an amplitude level substantially equal to that of the received difference signal S, and
de-matrixing the received sum signal M with the noise-reduced difference signal to obtain said left and right channel stereophonic signals.

1 more element

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.

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.degree. 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.

10 more elements

Dependencies are inferred from the claim text.

Compatible transmission techniques for FM stereophonic radio and television

Life of this patent

Compatible transmission techniques for FM stereophonic radio and television

Life of this patent

Abstract

Claims17