An improved audio signal processing system for use in an audio reproduction apparatus is described. The apparatus is of the type for generating ambient effects and includes at least two channels for respectively transmitting an audio signal to at least two speakers so that one of the speakers reproduces sound in response to the audio signal at a predetermined delay with respect to the other. The improved system comprises gain control means, electrically connected to receive the audio signal being transmitted to the one speaker, for controlling the signal gain of the system in accordance with the signal level derivative of the audio signal.