Abstract: An improved audio mixing system that does not instantaneously switch a microphone from the attenuated level to the unattenuated level in response to level changes on the microphone is disclosed. The system is not limited to one type of microphone and does not depend on separate sensing microphones to determine the background noise level. In addition, the active signal is not amplitude modulated by extraneous noise inputted through inactive microphones.

Abstract: An equalizing circuit is disclosed, in which a received signal is divided into high frequency components in different bands and a low frequency component; after having subjecting the high frequency components to a predetermined signal processing, they are amplitude-modulated, based on amplitudes thereof; and amplitude modulated signals thus obtained and the low frequency component are combined to obtain a synthesized signal. By effecting such a equalizing processing, it is possible to make the reproduced image quality of a video signal more distinct and to make an audio signal, whose band is restricted, have richer sound quality.

Abstract: A synchronous AM detector and processor requiring a reduced number of external components and fewer integrated circuit pins comprises an audio processor having a first filter operation controlled by a control voltage and an AM stereo decoder including a lock detector and a phase locked loop having a second filter operation controlled by the control voltage. A single control node is coupled to the audio processor and the phase locked loop, the control node providing the control voltage for the audio processor and the phase locked loop. The voltage at the control node is biased normally high, capable of being pulled low by the audio processing circuit and capable of being pulled low by the lock detector. An RC circuit decays the rise time of the control voltage at the control node after the control voltage has been pulled low. Circuitry is added to control the first filter operation of the audio processing circuitry responsive to the control voltage at the control node.