A compressed-bandwidth stereophonic system for radio transmission

The purpose of the system is to provide a stereophonic signal for radio transmission within a bandwidth only slightly greater than that required for ordinary monophonic transmission. The left and right microphone signals are combined to form a single a.f. signal which is available for ordinary monophonic reception. They are also processed in such a way as to emphasize the beginnings of sounds and then utilized to form a signal, with a bandwidth of 100 c/s, carrying the directional information only. This directional signal is caused to modulate a sub-carrier at a power level much lower than that of the a.f. signal. In the receiver the a.f. signal and the directional signal are applied to a Hall multiplier unit giving the required left-loudspeaker signal as one output and the right-loudspeaker signal as the other.