- An automatic control circuit which modifies the gain of a receiver at set intervals, so as to maintain the output signal levels within a desired amplitude, in response to varying input signals. To do so, it reduces sensitivity to strong signals, while increasing it for weak ones. Such modifications are usually anticipated, as when a loran receiver adjusts its gain between successive pulses from fixed transmitters. Its abbreviation is STC. Also called sensitivity-time control circuit, differential gain control, gain-time control, or gain-sensitivity control.