automatic level control (ALC)
Automatic Level Control(ALC), often referred to as automatic gain control, is an electronic circuit that keeps the output level of radios, car radios, tape recorders, or other entertainment equipment as constant as possible, regardless of input signal variations.
Automatic Level Control (ALC) uses nonlinear feedback to compare the level of the output signal with that of the input signal and derive a correction signal for gain control.
Automatic level control is also used in communications equipment. Since it affects voice quality there, the International Telecommunication Union( ITU) has drawn up Recommendation G.169 for network components to ensure network stability and minimize the influence of automatic level control on voice transmission.