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Everything you need to know about reverb

Digital Reverb Unit

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Audio engineers and music producers are often after a very direct sound. This is the reason microphones are typically placed very close to the source. This captures the source with a lot of detail but also takes out most of the natural ambiance of the room. Most producers usually prefer to use emulated spaces that are exaggerated. The ability to use multiple types of reverb with different tonalities helps give the production depth, contrast, and keep things interesting. It also helps engineers deliberately place certain sounds in a mix. For instance, I may want to drench the pad synth to make it sit further back in the mix so it doesn’t interfere with the lead synth line.

Panning gives us the ability to move sounds left and right, and time-based effects give us the ability to move sounds forward and back.

What is reverb?

Reverberation, more commonly referred to just as reverb, is the sound created when sound waves are being reflected and interacting with the world around us. The time it takes these reflections to dissipate or be absorbed into other objects is decay time.

When a sound is made in a room, what we are hearing is not just the sound directly from the source but also the waves reflecting off all the surfaces in the room that are then bouncing back into our ears. For instance, if someone yells at you, you’re not just hearing the waves coming directly from the person’s mouth but also how it is interacting with the physical surfaces and walls of the room you’re in.

I have a very early memory of asking why it sounded better when I sang in the shower. The highly reflective tile in most bathrooms creates a natural reverb that helps with your pitch, making it more fun to sing into. I always recommend when recording a vocalist to make sure they are monitoring their vocals with effects like reverb to create the best sound possible. If the artist sounds good in their headphones, it will yield a better performance than if they were monitoring only their dry vocals straight from the microphone.

The history of reverb

Artificial reverb, or reverb that isn’t the natural ambiance of the room you’re recording in, was first used in a musical production by Bill Putnum and Robert Fine in 1974. Both of these pioneering audio engineers separately came up with the idea to put a speaker in another room, record it with a microphone, and then mixed it back in with the original dry sound. Decay times were adjusted by changing the room acoustics or by moving the microphones. The problem is these require an entire room for just a single reverb, something we can do today with a free plugin.

Hammond started putting reverbs in their organs in 1940, and Fender began to put them in their amps in the late 1950s. Still, it wasn’t until 1957, when EMT released the 140 plate reverb, that studios were finally able to ditch the chambers that took up an entire room for something a little more practical. The 140 plate was the first artificial reverb that studios adopted because it had an incredible sound that could measure up to the finely tuned chambers that were found in the elite studios of the time. The 140 plate was an enormous success, and its sound is so coveted that developers continue to try and replicate the gorgeous sound. In 1976, the EMT 250 was released, the first-ever digital reverb, which opened the doors to seemingly limitless possibilities.

There are three ways an artificial reverb is commonly created. The first type of reverb available to recording studios required a physical or real element, such as an entire room or a humongous steel plate.

The next two types, algorithmic and convolution, are digitally based. With greater computer processing power came the ability to develop convolution reverbs, which use impulse response or IR samples recorded in real physical space by sending a burst of white noise into the room and recording the decay. This gives engineers the ability to capture and reproduce the sound of any room or their favorite plate or spring reverb. These impulse responses are designed to mimic the decay that was initially recorded, which makes them useful when trying to replicate a specific type of ambiance. This makes them extremely useful in post-production when you need to rerecord audio that was recorded somewhere else. An impulse response taken in the original location would allow the mix engineer to add in the same sound of the room when rerecording.

The second way digital reverb is created is through the use of algorithms. The EMT 250 is the first digital reverb ever made and was algorithmic based. I had the honor of talking with Bill Blesser, the original designer. You can view the entire article here. Algorithmic reverbs are created using a mathematical formula that is calculated and rendered by the processor in the hardware or your computer if its a plugin and then spit back out your speakers.

EMT 250 Digital Reverb

These are the 6 most important types of reverb you’ll need to know about.

Room reverb

You know what a room is, right?

Room reverbs to create the response of a… you guessed it… a room. Usually, a small room, as these reverbs, most commonly have a short decay time, typically under 1 second. This reverb can give the sound life and put it in a space that’s familiar to our ears. Because of this familiarity, it adds a pleasing effect to our ears and aids in getting sounds to fit together in a mix. I commonly find myself using room reverbs on drums, especially snares, percussion, and other acoustic instruments that are a bit too dry but don’t need a longer reverb with an audible decay. Because the decay time is so short, the reverb is usually felt rather than heard when putting it in a mix.

Plate reverb

Plate reverb, like the aforementioned legendary EMT 140, consists of an 8 x 4 x 1-foot wood box with a sheet of steel hanging inside. A transducer then sends the signal into the sheet of metal, which causes it to vibrate; the result is then picked up via another transducer and mixed back into the dry signal. The length of the decay is adjusted via a damping mechanism, which can also be controlled via a remote. When I interned at Trout Recording in Brooklyn, New York, owner Bryce Goggin had just purchased a 140 plate, but it didn’t have a remote. I fondly remember being assigned to go down to the basement to adjust the decay time whenever necessary.

Plate reverbs have a very pleasing sound and work well on pretty much everything. Sound waves travel faster in the metal plate than they do in the air, which gives them a higher density, smoother tail, and ultimately a very desirable sound that engineers and producers all over the world have grown to know and love.

Radio City Music Hall in New York City
The famous Radio City Music Hall in New York City.

Hall reverb

This type of reverb simulates a finely tuned concert hall. Concert halls are auditoriums that are designed with acoustics being the main priority. These halls are meticulously tuned to remove any negative artifacts that can be detrimental to the sound, such as rings, standing waves, and uneven tonal response. These are a classic artificial reverb that became popular with the rise of digital time-based effect units. Since these rooms are designed for optimal acoustics, it’s no surprise that they are often emulated. Halls can be used on just about anything with successful results. One of the most popular hall reverbs is the Lexicon 480L which can be found at many of the most esteemed studios around the world.


Chamber reverb is usually a small to a medium-sized room made up of different types of reflective surfaces strategically placed at different angles. A send and return are set up using speakers and microphones. Chambers offer a thick, dense and lush reverb without being overpowering. These are most commonly found on vocals and acoustic instruments but are great for any source that needs some character.

Echo chamber reverb

Spring reverb

Like a plate reverb, except instead of a sheet of metal, these use an actual spring. Spring reverbs most commonly have a short or medium decay time and is used on guitars and keyboards because they are small enough to fit into amplifiers. Don’t let that fool you; spring reverb can sound good on many different sources, including vocals, synths, piano, and of course, guitars. The sound can be described as metallic, like a plate but more lively, with less depth. 

The inside of a spring reverb tank-- Everything you need to know about reverb
The inside of a spring reverb tank.

They are most popular for the sproingy sound they make when you physically shake the reverb tank causing the springs to jostle around. Using a ton of spring reverb is a requirement when playing surf rock or producing dub music. In the late 1960s, AKG released the BX series of spring reverb units that became popular with recording studios.


These are extremely short reverbs, with reflections happening between half a second and shorter. This type of reverb is mostly used to add tone since the decay time is so fast, they are more likely to be felt rather than heard. Adding an ambient reverb return and sending multiple sources to it can have a nice gluing effect.

If you got this far, you finally know enough about reverb, maybe too much. Now it’s time to get out there and start reverbing!!! Put a reverb there. Put one over there. Put some reverb everywhere!

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EMT 250 and the birth of digital audio

EMT 251 at Sabella Studios
EMT 250

My experience with the EMT 250/251

When I started my first internship at Sabella Studios, the place was littered with strange things I’d never seen before. But nothing looked as strange as this black and red box that looked more like a spaceship control panel than recording equipment. That box was our EMT 251 that had been sitting in the corner of the control room and had built up an impressive collection of dust. We’re a small studio with a lot of vintage equipment, so it’s not uncommon for a piece of gear to be temporarily out of service, but this was different. No one was sure if we’d get this thing ever to work again. We could send it out to the one specialist in California who knew how to fix it, but it would cost us $1,500 just to have it looked at. As a small studio, we pride ourselves on doing just about everything in house, including the maintenance and repairs for all of our equipment. It’s how we’ve been able to survive for so long.

Opening the front of the unit to see hundreds of ICs doesn’t make the task of repairing it seem any easier. To make things even more difficult, EMT, the manufacturer of the box, scratched off any identifying part numbers to keep the ingredients of their mystical digital reverb a secret. Help came from an unsuspecting place: an intern led us to his father, an electronic technician, who was originally from Russia and didn’t speak any English. Fast forward a week or two, and he was at the studio with his oscilloscope, trying to figure out what was wrong with our 251. He decided to take it home to look at it further, and within a week, we had it back up and running.

It’s hard to imagine that the first version of any digital technology could be the best. It’s easy to see why earlier analog gear sounds better as there were better manufacturing techniques, lower cost of goods, and easier availability of materials which contributed to better overall build quality. In today’s digital world, everything eventually has a newer, bigger (or smaller), better, and more powerful upgraded model. The first version is never the best. How is it that the sound of the first digital reverb unit can still surpass even the most complex and expensive modern units?

I didn’t know, but I needed to find out…

Digital Audio

Digital audio is something everyone uses, from the home recording hobbyist to the professional recording studio. Recording digitally is built into the standard workflow when creating every genre of music. There was a time when nothing was digital, so how did the world go from entirely analog to just about completely digital? In modern music production, you don’t need to use any analog audio processing at all if you don’t want to.

The original reason people started to explore digital audio was for one reason: time based effects. Early in the history of recorded music, there was never an easy way to make delays and reverbs, except with expensive and large tools like reverb chambers, plates, and magnetic tape machines. There was a very limited amount of flexibility when it came to time based effects, which had become paramount to every single song on the radio since 1947 when Bill Putnam decided to put a speaker and microphone in his studio’s bathroom. Nowadays, we fire up whatever plugin we want, but before digital audio, you had to run it through a piece of hardware or mic in a physical space. Now how does it go from microphones in bathrooms to recording 48 tracks simultaneously into your laptop with a different digital effect on every track?

The EMT 250 was essentially one of the first plugins. It’s like if a Waves or Slate plugin you just bought came with a computer, interface, and converters and was all built into one box with the sole purpose of running that plugin, and with a $20k price tag, it certainly wasn’t cheap.

Dr. Barry Blesser

A Conversation with Dr. Barry Blesser

I had the pleasure of speaking with Dr. Barry Blesser, who is considered one of the grandfathers of digital audio. In 1974, Dr. Blesser oversaw the creation of the algorithm, and some of the hardware, for the first ever digital reverb unit.

Dr. Blesser was kind enough to speak with me and explain the history of digital audio and his involvement. He began the interview by telling me about Manfred R. Schroeder, a German physicist who worked at Bell Labs during the 1950s. Schroeder was the very first person to attempt digital signal processing. During this time, computer technology was so slow that digital was completely impractical. Processing a 3 minute piece of audio could take 24 hours. Although Schroeder’s experiments at this time were not of any practical use and were done completely out of curiosity and proof of concept, it did show that digital audio was possible.

Dr. Blesser then spoke of a chance encounter with Francis F. Lee, who would become the founder of Lexicon. “I was working in the MIT Labs at 3 in the morning because that was when I could get access to the minicomputers, and Frances Lee walked in. He was in the computer world; he didn’t know about anything digital audio. And I was in the [analog] audio world, so we bumped into each other at 3 in the morning and started brainstorming about how to merge these two. That’s how Frances Lee got started with Lexicon.”

Vintage ad for a later model of the Delta T-101

The result of this encounter was the first ever digital signal processor, the Delta T-101, released in 1971. Lee had been working on a digital heart monitor and, from Dr. Blesser’s suggestion, experimented with running audio through it. After a lot of experimentation, the result was a 100 ms audio delay line which could be used to help overcome live sound propagation delays or used as a pre-delay for plate reverbs. You put audio in, and 100ms later, it comes out. That was it. It was revolutionary at the time, but by today’s standards seems like just a step above useless. Steve Temmer, owner of Gotham Audio, commissioned Lexicon to make 50 units that he could release under the Gotham Audio name. A second version the T-102, was eventually released under the Lexicon name with an improved signal to noise ratio.

Throughout the 1960s, Dr. Blesser worked with EMT on many of their analog audio products. “They rejected the idea of doing real digital audio until Francis Lee started Lexicon. After Lexicon was successful with the T-101 they got pissed, and they said, ‘ok, we want to be in that business.’”

Peter Bermes, an industrial designer working for EMT, recalls the initial meeting to plan and brainstorm the EMT 250 involved nine people seated at a roundtable. The meeting, which went on to be the catalyst for the first reverb, Bermes says, took only 4 hours. The meeting occurred in 1974 at the EMT plant in Kippenheim, Germany. Among the group were Erich Vogl, Karl Bäder, Barry Blesser, and Peter Bermes. Dr. Blesser, along with a team of engineers, went to work on developing an algorithm they could use for practical digital reverberation. Only having the 100 ms delay box and Manfred Schroeder’s experiments, Dr. Blesser’s team built a simulator that could be programmed to run different reverb algorithms for testing purposes. After about two years of research and development, the EMT 250 was ready, and 250 units were produced.

So that doesn’t explain why the reverb still holds up in today’s world of endless digital options and newer upgraded algorithms, and more advanced convolution technology. It comes down to the sound. It just sounds good. Forget all of the pioneering and innovation that took place to develop this device. Even if this unit was introduced tomorrow instead of in 1976, it would still hold up as being a great sounding reverb, and that’s just a testament to the designers. Most of all, they made sure it sounded good.

Luckily, you don’t have to spend $20k to get the amazing sound of a 250 anymore. Universal Audio had Dr. Blesser reverse engineer the whole algorithm so they could model it in their 250 plugin. Although Dr. Blesser said that he did not hear it for himself, he was told it was completely bit accurate.

Related articles:
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Things I wish I learned sooner about audio engineering
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