A method available on some audio recorders and the audio section of video cameras in which audio levels are automatically controlled. On quiet passages, the camera raises the gain (raising the noise floor), and on loud passages, it will reduce the gain. You can hear this pumping of the gain in the soundtrack. In a pinch, its acceptable to use AGC, however, set levels manually whenever possible. If your camera offers a limiter option, that is a better way to deal with unexpected peaks.