Adaptive expanders for FM stereophonic broadcasting system utilizing companding of difference signal

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, unchanged, difference signal is used as a reference signal for controlling the expansion of the compressed difference signal so as to cause the amplitude of the companded difference to equal the level of the usual difference signal. Thus, the expander is adaptive to any compression characteristic that might be employed at the transmitter. Further, the availability of the usual uncompressed difference signal at the receiver enables the adaptive decoding of dynamic parameters of the received signal, such as frequency response and attack and recovery times, so that all of the parameters of the original signal can be restored automatically.

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