An automatic gain control circuit is provided for an input signal in the form of a dc reference level and a superposed amplitude modulated ac data signal. A feedforward AGC loop has a low pass filter for deriving the level of attenuation from the attenuated dc reference level. A multiplier value (G) is based on the reciprocal of the level of attenuation (α) and this multiplier enables an output signal to be generated comprising a constant multiple (DG) of the input signal.