Automatic gain control

Automatic gain control (AGC; also called automatic voltage gain) is a closed-loop feedback regulating circuit, the purpose of which is to provide a controlled signal amplitude at its output, despite variation of the amplitude in the input signal. The average or peak output signal level is used to dynamically adjust the input-to-output gain to a suitable value, enabling the circuit to work satisfactorily with a greater range of input signal levels. It is used in most radio receivers to equalize the average volume (loudness) of different radio stations due to differences in received signal strength, as well as variations in a single station's radio signal due to fading. Without AGC the sound emitted from an AM radio receiver would vary to an extreme extent from a weak to a strong signal; the AGC effectively reduces the volume if the signal is strong and raises it when it is weaker.