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A reverb effect, or reverb, is an audio effect applied to a sound signal to create or simulate reverberation. It may be created through physical means such as plate reverb or effects unit, or with software.
The first reverb effects created for recordings used a real physical space as a natural echo chamber. A loudspeaker would play the sound, and then a microphone would pick it up again, including the effects of reverb. Although this is still a common technique, it requires a dedicated soundproofed room, and varying the reverb time is difficult.
A plate reverb system uses an electromechanical transducer, similar to the driver in a loudspeaker, to create vibrations in a large plate of sheet metal. The plate's motion is picked up by one or more contact microphones whose output is an audio signal which may be added to the original "dry" signal. In the late 1950s, Elektro-Mess-Technik (EMT) introduced the EMT 140. Popular in recording studios, this system contributed to many hit records such as Beatles and Pink Floyd albums recorded at Abbey Road Studios in the 1960s, and others recorded by Bill Porter in Nashville's RCA Studio B. Early units had one pickup for mono output, and later models featured two pickups for stereo use. The reverb time can be adjusted by a damping pad, made from framed acoustic tiles. The closer the damping pad, the shorter the reverb time. However, the pad never touches the plate. Some units also featured a remote control. The EMT 140 weighs 400 pounds (180 kg), 600 pounds (270 kg) in manufacturers shipping crate.
A spring reverb system uses a transducer at one end of a spring and a pickup at the other, similar to those used in plate reverbs, to create and capture vibrations within a metal spring. Laurens Hammond was granted a patent on a spring-based mechanical reverberation system in 1939. The Hammond Organ included a built-in spring reverberator.
Spring reverberators were once widely used in semi-professional recording and are frequently incorporated into Guitar amplifiers due to their modest cost and small size. One advantage over more sophisticated alternatives is that they lend themselves to the creation of special effects; for example rocking them back and forth creates a thundering, crashing sound caused by the springs colliding with each other.
Digital reverb uses various signal processing algorithms. Since reverberation is essentially caused by a very large number of echoes, simple reverberation algorithms use several feedback delay circuits to create a large, decaying series of echoes. More advanced digital reverb generators can simulate the time and frequency domain response of a specific room (using room dimensions, absorption, and other properties). In a music hall, the direct sound always arrives at the listener's ear first because it follows the shortest path. Shortly after the direct sound, the reverberant sound arrives. The time between the two is called the "pre-delay."
Reverberation, or informally, "reverb" or "verb", is one of the most universally used audio effects and is often found in guitar pedals, synthesizers, effects units, digital audio workstations (DAWs) and VST plug-ins.
Convolution reverb is a process used for digitally simulating reverberation. It uses the mathematical convolution operation, a pre-recorded audio sample of the impulse response of the space being modeled, and the sound to be echoed, to produce the effect. The impulse-response recording is first stored in a digital signal-processing system. This is then convolved with the incoming audio signal to be processed.
- Eargle, John M. (2005). Handbook of Recording Engineering (4 ed.). Birkhäuser. p. 233. ISBN 0-387-28470-2.
- Laurens Hammond, Electrical Musical Instrument, U.S. Patent 2,230,836, granted Feb. 4, 1941.
- December 2020, Stuart Williams 31. "How Genesis's Peter Gabriel and Phil Collins stumbled upon the '80s gated-reverb drum sound". MusicRadar. Retrieved 2021-06-19.