Abstract: A circuit for eliminating noise from a regenerated audio signal by detecting slope of the signal. A sensor senses an edge of a head switching pulse signal to thereby generate a predetermined control pulse. The circuit has a holder for holding a state of the regenerated audio signal in response to the control pulse and permitting charge or discharge of the held signal under a given control. A slope detector detects a slope from a fixed band of the audio signal and feeds back the detected slope to thereby control charge/discharge at the holder to alter the held signal level.

Abstract: An automatic gain control circuit for controlling gain according to a sound gain controller so as to output a stable video intermediate frequency signal includes a first gain control amplifier receiving a video intermediate frequency signal, for amplifying the signal by a sound gain control voltage and for then producing an amplified video intermediate frequency signal, a second gain control amplifier receiving a carrier signal having a sound intermediate frequency signal and a video intermediate frequency signal, for amplifying the carrier signal by the sound gain control voltage and for then providing the amplified carrier signal, and a sound gain control voltage detecting circuit for receiving the amplified signal from the second gain control amplifier, for detecting the sound gain control voltage and for then providing the detected sound gain control voltage to thereby automatically control the gain of said first gain control amplifier.