The effect of an abrupt sound dying away gradually, as if played in a medium-to-large space with hard, reflective walls such as a ballroom, concert hall, or cave. Today, most reverb used in recorded music is produced electronically, by digital devices that employ various mathematical methods. In the past, several electromechanical methods have been used including:
- Echo chamber: a room with hard floors, walls, and ceiling placed at odd angles determined by mathematical formulas. A signal is fed into the room via a loudspeaker, and the reverb picked up by one or more microphones placed in the room. Known for producing good-sounding reverb, but very expensive to do properly.
- Plate reverb: the signal is injected into a large metal plate via a transducer at one edge. The signal reflects internally within the plate, producing the reverb, which is picked up by other transducers along the other edges. Heavily used by recording studios in the 1970s, but expensive.
- Spring reverb: the signal is injected into one end of a metal spring by a transducer, and picked up by a transducer at the other end. Widely used in guitar amplifiers, organs, and some modular synthesizers. Spring reverbs are notorious for their rather unnatural-sounding reverberation, and for producing "boing" sounds if the spring unit is physically disturbed. But prior to the advent of inexpensive digital reverb units, they were the only reasonable means of producing reverb on a budget.
Reverb is usually produced electronically using a combination of delay lines of different time lengths, and filtering. An alternative approach is to use convolution to impose the response characteristics of an electromechanical method on a digital signal.