Reverberation is an acoustic effect that takes place when the acoustic energy generated from a noise emitting source is sent back by the surfaces (floor, walls and ceiling). It occurs when the sound is reflected on those several surfaces and is then heard with the referred "reverb" effect. In most cases, the reverberation time should ideally be reduced, so that the "reverb" effect is not perceived by the receiver. However, there are places where some reverberation must be added to help propagate the sound, such as in auditoriums.