Abstract: A decoder for use in an FM stereo broadcasting system in which the usual difference signal S and a compressed version S' of the difference signal are transmitted, automatically selects on a continuous basis for de-matrixing with the received sum signal M either an attenuated signal S' or the usual difference signal S based on the protocol that the attenuated signal S' is always selected unless the usual difference signal S is higher in level than a predetermined threshold potential related to the signal level at the knee of the expansion characteristic. The decoder eliminates the need for the relatively expensive analog variable gain amplifier used in prior art decoders and is less sensitive to time constant errors and errors due to multipath distortions.

Abstract: An FM stereophonic broadcasting system incorporating companding of the difference signal in which the broadcast signal includes both the usual difference signal and a compressed version of the difference signal which utilizes, in the transmitter, a circuit for simultaneously compressing the difference signal according to a desired characteristic and modulating the compressed difference signal onto a carrier and, in the receiver, essentially the same circuit for simultaneously demodulating and expanding an incoming compressed difference signal. Simultaneous compression/modulation is achieved by multiplying the difference signal, the carrier signal and a gain control signal, preferably derived from the output signal from the multiplier, for determining the compression characteristic, thereby producing at the output of the multiplier the carrier modulated with the difference signal compressed according to a desired characteristic.

Abstract: In the receiver of an FM stereo broadcasting system which transmits both the usual stereo difference signal S and a compressed version S' of the difference signal compressed according to a compression characteristic such that signals in a lower portion of the audio frequency spectrum are not compressed and signals having frequencies above said portion are compressed, according to a desired characteristic, instead of complementarily expanding the compressed difference signal, only those signal frequencies that have been compressed at the transmitter are expanded.

Abstract: The compatibility of an FM 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, with conventional FM receivers is improved by minimizing crosstalk from the compressed difference signal to the usual difference signal that sometimes occurs in conventional FM stereo receivers, particularly when the multiplex signal is received under multipath propagation conditions.

Abstract: To counter the effects of multipath on the signal received at the receiver of an FM stereophonic broadcasting system utilizing companding of the stereo difference signal, the normal operation of the expander embodied in the receiver is automatically modified in response to detection of multipath so as to minimize such effects and thereby improve the quality of the reproduced signal. In the preferred embodiment, a substantially fixed or steady control voltage replaces the normal dynamically varying control signal for the variable gain element of the expander during occurrences of multipath disturbances in excess of a predetermined severity. Another aspect of this embodiment is that a D.C. correction voltage having an amplitude proportional to the severity of the detected disturbances is combined with the fixed control voltage for the variable gain element in a manner to reduce the gain of the element thereby to further reduce the effect of the disturbance.