A system in which the output amplitude is used for automatic control of the gain of an amplifier. Seismic amplifiers used to have individual AGC for each channel, although multichannel control was sometimes used. See Figure A-25 and gain control. Also called automatic volume control (AVC).
FIG. A-25. Automatic gain control
(AGC) action. (a
) Input; (b
) output. AGC gradually restores the output to the same level after an increase or decrease in input amplitude.