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.