a) Circuitry used to ensure that output signals are maintained at constant levels in the face of widely varying input signal levels. AGC is typically used to maintain a constant video luminance level by boosting weak (low light) picture signals electronically. Some equipment includes gain controls that are switchable between automatic and manual control.

b) Electronic circuitry that compensates for either audio or video input level changes by boosting or lowering incoming signals to match a preset level. Using AGC, changing input levels can output at a single constant setting.

c) A feature on most video cameras and camcorders that, when engaged, boosts the signal to its optimum output level. Automatic gain control (AGC) is available for video, and less frequently audio use.