PURPOSE: To record the interchangeable 4-channel sound information, by modulating a subcarrier with a subchannel signal and using a signal obtd. by processing the main carrier by the FM processing with a signal superposed on a main channel signal.

CONSTITUTION: For FM modulators 11 and 12, the frequency shift is set at ±100kHz for modulation of a main channel signal. While the frequency shift is set at ±45kHz in a monaural mode and at ±60kHz in a stereo mode respectively for modulation of a subchannel. This subchannel signal is obtained by applying FM modulation to the subcarrier by modulators 9 and 10, and the frequency of this subcarrier is set triple as high as a horizontal synchronizing frequency. At the same time, the main carrier is set at 1/4 offset to the horizontal synchronizing frequency. This minimizes generation of beats to a reproduced screen due to an audio carrier.