Imagine that when it is too quiet, it will take say 5 seconds to come up to volume and visa versa. Since the change in volume of the material drives its automatic gain control (AGC), it can not work until the change on the input side has happened. To keep the dynamics of the music from causing it to "pump" (where it sounds like someone turning the volume knob to the beat), it has a long delay on the volume control. If you look at compressors (a similar item) there often are controls for attack and decay which sets how long it takes for the compressing action to take place. The manual for this doesn't mention the numbers for this device, but I would have to guess a few seconds otherwise it could get false readings from drums or the like.