These days, we’re a bit spoiled with the sophistication of reverb plug-ins. Modern algorithms, like those pioneered by iZotope's own Exponential Audio reverbs, are able to create lush and realistic reverb spaces, while some convolution reverb plug-ins are able to recreate specific real-world spaces. However, we obviously haven’t always had access to these reverb tools, as music producers have been effectively using the properties of space in their work for decades.
In this article, we’ll follow the development of artificial reverb from echo rooms to the modern convolution reverb plug-ins of today. While each advancement in reverb technology generally improved upon existing techniques, each technique has its own sound and can be viable in music production today.
Before we discuss artificial reverb, it’s important to understand why we even want to add reverb in the first place.
A product of acoustics, natural reverb has been an important component of music for centuries. Concert halls were (and are still) specifically designed to control the propagation of reverberant signals in the room. This is done to redirect sound waves to the audience, creating a lush ambience in which the music occurs and is experienced.
Spaces like Boston’s Symphony Hall are regarded for the ambience they create, captivating audiences for years. Reverbs such as PhoenixVerb, NIMBUS and Stratus 3D all help establish a natural, pure and transparent reverb.
A sense of space makes music sound more “real” and organic, an important fact given that live “real” music has been popular for centuries. Therefore, as music consumers like the sound of reverb, this “technique” transitioned from live music to recorded music.
Natural reverb in music is simply achieved by recording in a reverberant space, a space which creates room noise that’s captured in the recording.
Because the reverb must be captured in the recording process, studios invested in custom-built recording rooms to achieve the sound that they were after. Famous spaces like the main recording room in Columbia Records’ 30th Street Studio, renowned for their reverberant signatures, were utilized as the reverb source for some of the most famous projects in music (the legendary 1959 Kind of Blue album from Miles Davis was recorded at 30th Street).
In a natural reverb context, the dry / wet balance is determined by the distance between the microphone and the sound source. By playing close to the microphone, dry signal is relatively louder than the room noise, leading to a dryer recording.
Playing further from the microphone causes direct sound from the sound source to blend with the room noise. With the room playing a larger role in determining which sound waves reach the microphone, a wetter sound is created.
From the onset of recorded music, recording engineers were playing with these techniques to include reverb in recordings. However, reverb’s use in recorded music was generally limited by speaker technology available to music consumers.
Early jukeboxes, popular music sources introduced in the 1920s and 1930s, did not respond well to room reverb due to their speaker quality. This led to a period of music from the 1930s to the 1950s in which tracks in general, and vocals in particular, were quite dry.
The dry character of Bing Crosby records showcases this trend quite well.
As technology improved, however, room reverb became viable and in-vogue again. Natural reverb was and continues to be an important tool in music, especially in genres centered on live performance like jazz and classical.
Echo rooms and chamber reverb
The biggest issue posed by natural reverb is that the reverb signal is inextricably tied to the recording. Once the recording is printed, the dry / wet balance cannot be adjusted or modulated over time. And if you got the perfect take but there were problems with the reverb, tough luck. Guess you have to wait a few decades for RX De-reverb to come out…
Audio production pioneer and legend Bill Putnam Sr. solved this dilemma in 1947, being the first person to use artificial reverb creatively in a pop song. He did this in The Harmonicats’ “Peg o’ My Heart,” in which he utilized an echo room. This technique would come to be known as “chamber reverb.”
Chamber reverb first requires a room. In many professional studios, the room would be empty, made of concrete, and underground. This creates an isolated and measurable reverberant space. The room can vary in shape, size, and materials according to the studio’s needs.
An echo room can be anything from a custom-built room to a spare room in the studio (Putnam’s echo room for “Peg o’ My Heart” was the studio bathroom—listen for the short reverb tails attached to the harmonicas and guitar).
A loudspeaker is placed in the room. Audio signal is sent from the mixer to the loudspeaker, which plays audio into the room. This triggers the room acoustics to create a specific reverb sound. A microphone in the room then records the reverberant signal and sends it back to the mixer.
Now, recording and mix engineers had an isolated reverb signal to manipulate. The flexibility to separately process dry and wet signals and set dry / wet balance during the production process was a crucial development in audio production.
If you’ll notice, this system is very similar to a reverb return reverb track in the modern music production environment. This echo room process was the first development in the concept of sends and returns in audio production. The benefits introduced in the development echo rooms carry over to the benefits of using return channels today.
Mechanical reverb systems
Unfortunately, the characteristics of reverb signal (i.e. decay time, timbre) generated by an echo room are relatively non-adjustable, as reverb is totally dependent on the room.
Also, building a room (or several rooms) for the purpose of being empty and generating reverb is costly and takes up space. As a result, mechanical reverb systems were created to achieve similar results, give engineers additional control, and minimize costs and building permits.
The first of these systems was spring reverb. This was initially introduced as a feature in Hammond Organs in the 1930s and 1940s. As these organs were sold mostly for home use, and as people were accustomed to the reverb of a church space when hearing organs, consumers wanted an effect to replicate this reverb.
Laurens Hammond, developer of the Hammond Organ, created this effect by repurposing a device designed at the pioneering Bell Labs. This device used springs and wire to simulate the delay experienced during long-distance calls. Hammond used this concept and similar materials to create a delay-based reverb effect called spring reverb.
The “sound” of reverb is caused by a series of reflections, which occur as sound waves bounce off of surfaces. The blur of these reflections blending with each other causes the smooth tail that we typically associate with reverb. Using delays as this series of reflections, a spring reverb is capable of creating convincing artificial reverb.
A spring reverb unit works similarly to a plate reverb, replacing the sheet metal plate with a set of metal springs. A transducer on one end excites the springs with audio signal, causing them to vibrate along the length of the springs.
As some vibration remains in the springs, a series of rapid delays of the original signal occurs. A pickup on the other end of the springs records the series of delays, which is functionally similar to the series of reflections found in natural reverb.
The first spring reverbs generally housed the springs in tubes filled with oil, which help to dampen the vibrations. Different amounts of oil would cause the springs to stop vibrating at different times, effectively controlling the reverb decay.
By the 1960s, Hammond had developed the technology to the Hammond Type 4 reverb unit, a spring reverb unit that could fit inside a guitar amp. The technology was therefore licensed for use in Fender guitar amps, as well as Moog and Buchla modular synth systems.
Spring reverb’s gritty and clangorous qualities made it popular for genres like rock, dub, and reggae, making it an especially popular effect for snares and guitar. As spring reverb has an industrial sound, it is now mostly used as a particular effect rather than a go-to technique for standard reverb sounds.
For an explicit example of spring reverb in action, check out “Dub You Can Feel” by King Tubby. In the snare fill during the first couple seconds and at other points, the snare is run through a spring reverb. Listen for the raw sound of the spring reverb.
The other famous example of a mechanical reverb system was plate reverb. German company Elektro-Mess-Technik (or EMT) introduced one of the legendary pieces of audio technology, the EMT 140 reverb unit, in 1957. Instead of using a physical space to create the sound of reverb, a plate reverb unit takes advantage of sound waves resonating in a solid object.
Standard plate reverb units are centered around a large, thin piece of sheet metal. This “plate” is suspended using a metal frame and a series of springs. A transducer introduces vibration into the sheet metal according to the input signal. This vibration is then recorded with either one or two pickups, which respectively create a mono or stereo recording. A damping plate is able to control the duration of vibrations in the metal plate, which translates to reverb decay time.
The vibration in the metal plate creates a slightly different, but similar effect to physical reverb. While not identical to natural reverb, plate reverb sounds convincing and has a warm sound that people continue to love. As a result, plate reverb played a major role in many productions done in the second half of the 20th century.
“Time” by Pink Floyd is a great example of the EMT 140 in action.
Digital reverb systems
With the introduction of digital audio, reverb technology continued to develop. Instead of using physics to create reverb, digital reverb systems could use algorithms based off of physics to recreate accurate reverb effects.
By using a series of delays (with the level, frequency content, and timing of which being controlled by mathematical algorithms), digital reverb units can effectively reproduce the effect of a natural reverb tail.
EMT (the same company that created the first plate reverb) introduced the first commercial digital reverb system in 1976. The EMT 250 Electronic Reverberator Unit not only contained a highly adjustable reverb processor, but also the capabilities to apply effects like chorus, phasing, and delay.
Invented by Dr. Barry Blesser (who also helped launch Lexicon, another industry titan in early digital reverb technology), the EMT 250 is still regarded as one of the best-sounding digital reverb units of all time. Considering its early introduction into the audio technology sphere, its longevity and sound are especially impressive.
The EMT 250 was quickly updated with the EMT 251, which offered an LCD display and several improvements to frequency response and parameter control.
In 1978, Lexicon introduced the Lexicon 224. This unit contained many of the EMT 250’s features but was about half of the 250’s $15,000 price tag, and therefore found its place in many professional studios.
The development of digital reverb also saw the introduction of convolution reverb into the music production realm. Sony released the first real-time convolution unit with the DRE-S777 in 1999, allowing for more organic results than purely algorithmic units. For more information on convolution and convolution reverb, check out our article on the topic.
Digital reverb units did not entirely replace mechanical reverb technologies (like plate and spring reverb), but instead added a further tool for engineers to use. However, with the general trend moving from analog audio to digital audio, coinciding with the development of more sophisticated digital reverb systems, digital reverb continued increasing in popularity through the introduction of software-based reverb.
Software reverb plug-ins
The reverb technologies that we’ve discussed so far all had one thing in common: they were cumbersome. Natural reverb and echo rooms obviously posed a construction obstacle, while most mechanical and digital units were large and awkward (floor-standing digital units like the EMT 250 even weighed around 600 lbs).
The movement to digital audio helped to solve these problems, as software-based reverb plug-ins slowly became the new norm. Like their digital hardware counterparts, software reverbs are either algorithmic or convolution-based, and implement many of the same processes. With the ever-accelerating development of audio technology, reverb plug-ins have become powerful and sophisticated enough to rival even the results of natural reverb.
This is where people like Michael Carns, founder of Exponential Audio, really shine. Explore Exponential Audio's nearly dozen software reverb plug-in options.
Over the course of music production history, artificial reverb has become a cornerstone of the production process. Each iteration of artificial reverb introduced new processes and sonic possibilities for producers, ultimately shaping the music that people have loved for decades.
And even with the power of modern reverb plug-ins, it’s tough to declare that this is the final development in reverb technology. Technological advancements will continue and engineers will continue to create amazing work using them.