The Room That Wasn't There: Reverb and Imaginary Architecture in Electronic Music
Electronic music has no natural acoustic environment. A synthesizer generates a signal in the electrical domain. No room is involved, no air displacement occurs during the production process, and no surfaces reflect or absorb the sound. The signal that emerges is acoustically bare, a waveform with frequency content but no spatial information.
The reverb unit exists to solve this problem. Its function is to fabricate a room that does not exist and to place a sound convincingly inside that imaginary architecture.
The Physics of the Real Room
Natural reverberation is the composite effect of a sound source's direct signal and the many delayed reflections of that signal returning from surfaces in an enclosed space. When a hand claps in a cathedral, the direct sound arrives at the listener's ears first, followed within milliseconds by early reflections from the nearest surfaces, then by a dense cloud of later reflections accumulating as sound energy bounces between walls, floor, and ceiling.
The character of a real room's reverb is a function of the room's physical dimensions, the absorption coefficient of its surfaces, and the position of the sound source relative to the listener. A stone cathedral produces a reverb tail decaying over several seconds. A recording studio lined with acoustic foam produces a reverb so brief as to be nearly imperceptible.
The Spring
The first practical reverb units used a different physical phenomenon to approximate this effect. Spring reverb, developed in the 1930s and widely deployed in guitar amplifiers from the 1950s onward, sends an audio signal into the mechanical vibration of a spring, where it propagates at the speed of mechanical waves in steel rather than at the speed of sound in air. The signal travels to the far end of the spring and returns, superimposed on itself at a delay determined by the spring's mass and tension.
The result is not a convincing room simulation. The spring imposes its own physical character on the signal, producing a bright, metallic shimmer that corresponds to no actual architectural space. Producers working with spring reverb were not simulating rooms. They were discovering a class of acoustic event with no physical analog.
The Plate
EMT's 114 plate reverb, introduced in 1957 and standard in professional recording through the 1970s, improved on the spring by using a large suspended sheet of steel. Sound feeds into the plate via a transducer, propagates through the metal as mechanical waves, and is picked up at a separate point by a second transducer. Because the plate is large and wave propagation is complex, reflections become dense quickly, creating a smoother reverb tail.
The EMT 114 plate became the default reverb sound of mid-century American professional recording. The warmth associated with recordings of this era is partly attributable to the acoustic character of the steel plate, which attenuates certain high frequencies during propagation. The plate colors the signal toward the warm end of the spectrum, a consequence of the physics of mechanical wave propagation in steel rather than of any deliberate aesthetic decision.
The Algorithm
Digital reverb, beginning with the Lexicon 224 in 1978, replaced mechanical systems with mathematical models of acoustic decay. Instead of propagating a signal through a physical medium, an algorithm generates a dense network of delays of varying length and amplitude designed to mimic the pattern of reflections in a real or imagined space.
The Lexicon hall algorithm does not simulate a specific hall. It generates a statistical approximation of the average properties of a class of large reverberant spaces. The resulting sound is more idealized than any real room, a Platonic architecture accessible only in the digital domain.
Electronic musicians discovered that this idealized space, precisely because it corresponds to no real room, sounds more appropriate to synthesized sound than any simulation of genuine architecture would. A room that does not exist is the correct environment for a sound that could not exist either.