Abstract: Automatic gain control circuit comprising amplifier means (10) which produce an output signal that has an amplitude controlled by a control signal (CT). Recursive filter apparatus (20) (22) measures the power of the output signal and yield a measure of power which is compared (24) with a window of permitted power values to generate the control signal (CT). Depending on the result of the comparison, an initialization signal (INI) is transmitted which enforces a reference power value on a recursive filter to accelerate the gain control. Utilization in apparatus that use signals that have fast and considerable amplitude variations, as in digital modulation signal receivers.