Abstract: A four-channel stereo receiver capable of making the four-channel indication, and automatically changing over the four-channel mode operation and the two-channel mode operation or muting the monaural and the two-channel signal, based on the presence or absence of at least one of the second and the third sub-channel signals, and the second pilot signal included in the four-channel composite signal but not in the two-channel composite signal.

Abstract: A 4-channel stereophonic demodulating system based on a switching mode, which comprises a plurality of switching means for demodulating a received 4-channel stereophonic composite signal under control by a first and a second switching signals obtained from a pilot signal, means to separately derive four stereophonically related signals at the respective output terminals of said switching means, and adding means to add plural output signals from at least one switching means to each other. The signal levels of the individual channel signal components are adjustable by said adding means relative to one another to enable separation adjustment, so that in each of the four stereophonically related signals which appear at respective output terminals of the system, cross-talk due to the other signals is reduced.