Reverberation is the continuation of a particular sound after the original sound is removed. When sound is produced in a space, a large number of echoes build up and then slowly decay as the sound is absorbed by the walls and air, creating reverberation, or reverb. This is most noticeable when the sound source stops but the reflections off walls, curtains, carpets etc continue, decreasing in volume until they can no longer be heard. A reflected sound wave like this will arrive a little later than the direct sound, since it travels a longer distance, and is generally a little weaker, as the walls and other surfaces in the room will absorb some of the sound energy. Shortly after the direct sound, the reverberant sound arrives. The time between the two is called the 'arrival time gap'. This gap is important in recorded music because it is the cue that gives the ear information on the size of the hall, better digital reverbs can incorporate this arrival time gap and hence sound more realistic.

Chamber reverberators
The first reverb effects were created by placing a loud speaker and a microphone in a real space such as a hall using that space as a natural echo chamber. The mike would pick up the sound from the speaker including the reverberated sound. To make the effect stronger the walls of the room are covered with sound-reflecting discs or other similar materials. By changing the position of the speaker and the microphone it is possible to get some variations in a recorded sound. The down side of this technique is that it is difficult to vary the reverb time.

Plate reverberators
A plate reverb system uses an electromechanical transducer. The transducer is a device which converts electrical voltage variations representing music or speech, to mechanical vibration. The transducer creates vibration in a large plate of sheet metal. A pickup captures the vibrations as they bounce across the plate, and the result is output as an audio signal. It was...