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 . additional circuitry is added to control the second filter operation of the phase locked loop in response to the control voltage level .