Abstract: In a loudness control circuit, the output DC voltage of a first variable DC voltage source is applied to a first amplifier for increasing volume to vary the gain of the latter, and to first and second differential amplifiers, while the output DC voltages of second and third variable DC sources are applied to the first and second differential amplifiers to provide difference voltages, which the applied to second and third tone control amplifiers which amplify the low and high frequency ranges, respectively, to control the gains thereof, so that the components of the sound in the low and high frequency ranges are boosted, thus achieving the weighting.

Abstract: In a noise cancelling system for FM receivers, means is provided whereby a pilot signal of 19 KHz is always detected from a stereo composite signal, whether or not a noise canceller circuit is operated. The 19 KHz pilot signal is injected into a phase locked loop, and a signal of 38 KHz in synchronism with the 19 KHz pilot signal is generated which in turn is injected into the multiplex demodulation circuit. Furthermore, means may also be provided which eliminates, from the 19 KHz pilot signal, noise mixed into the stereo composite signal and having a frequency characteristic of (19/n) KHz (n=1, 2, . . .) and then detects the foregoing pilot signal, thereby achieving satisfactory stereophonic separation.