Most recordists use digital reverb these days, but a lot of the programming of a digital reverb is based on either environmental reverb or mechanical reverb simulators.
Environmental Reverb - sound waves bouncing around a hall or a room, or a reverb/echo chamber.
Mechanical Reverb Simulators - using metal and speakers and pickups to “mimic” naturally occurring acoustic reverb.
This article covers Live room, Chamber, Plate and Spring reverb — how they sound, how they work, where you might find them useful in a recording, etc. There are some musical examples to listen to, and we've made a “cheat sheet” for our Micro Digital Reverberator that will help you when you select programs on it.
But first...
Quick Explanation of Reverb
Highly technical and scientific diagram...
A sound travels out from a source, moving at the speed of sound, which is about 1’/ms (one foot per millisecond). It strikes a surface, like a wall or a cliff, bounces off of it and comes back to our ear, still moving at the speed of sound. If the wall was 20’ away, it would take about 20ms for the sound to travel to the wall, and then another 20ms to travel back. The total time of the echo would be 40ms. If the wall absorbed a bunch of the sounds high end, the echo would sound less bright.
Reverb isn’t one sound wave bouncing off one surface. It’s sound waves bouncing off floors, ceilings, walls, tables, chairs, people, etc. Reverb is thousands, even millions of echoes that happen over a period of time. Rather than hearing a distinct, clear echo, we hear a wash of sound that gradually decays over time as the sound waves are absorbed by the surfaces off of which they bounce. The frequency response of the reverb is caused by the absorption of different frequencies by the surfaces of a space. A big wood room with carpets will absorb fairly evenly, with the highs being absorbed the most. A small tiled room will tend to sound bright because more high frequencies are reflected by the tile rather than absorbed.
You can download our Cheat Sheet here. And here’s a quick thing to try: Get a vocal track, put an MDR on it, and cycle through the programs' marked chamber and then listen for the qualities that are common to all the chamber presets. Do the same for plates, and then for springs, then for live spaces. You'll teach yourself to hear the differences, and then hearing reverb types on recordings, and making choices for your own mixes will be a lot easier.
Alright, enough of that. Onward.
Halls and Room - natural reverb
Big concert halls and large rooms work well with sounds that have slow transients, like strings and orchestras. Big rooms can make drums and percussive sorts of parts sound confused and muddy. As room sizes get smaller, they become useful for adding character or thickening. Small rooms can also sound very weird and kinda ugly.
Studio in the early '70s. Note they’re setting up a mic to pick up the whole room.
The earliest type of reverberation on recordings was caused by the space in which the recording was made. If an orchestra was recorded in a concert hall, the sound of the reverb of that hall would get recorded as well. Ditto for recording anything in live studio space, a little vocal booth, a stairwell or a bathroom, etc.
Concert halls tend to be warm sounding, without an emphasis on highs, and have decay times over 2 seconds. As a natural space gets smaller, it tends to get brighter and a bit wonky sounding. Concert halls are designed with certain frequency response and decay characteristics, while stairways and bathrooms aren’t designed with any thought of acoustics.
To my ears, the decay time of most real spaces - halls, live rooms, have a logarithmic decay time. That is, the reverbs' energy drops off drastically and then slowly tapers away. It sounds like this diagram looks:
There is almost always a hint of the room on any recording made with a microphone, and sometimes that hint is quite pleasant, and sometimes it sucks. A little bit of room on an instrument or vocal can add a subtle doubling effect and make the instrument sound bigger (check out this article here). A room with a lot of character — a bathroom, a hallway, can make a part stand out.
Here’s an orchestral recording of some Iron Maiden. Note that the drums are boxed in with plexiglass. Live drums in a highly reverberant concert hall would be rather unintelligible.
Another thing to listen to: this Cowboy Junkies’ track was recorded basically live in a church around a stereo mic.
Reverb Chambers
Chambers are usually bright and have a rhythmic, repetitive quality to the decay. Chamber reverb is a classic sound on vocals, and putting chambers all over a recording will impart a vintage quality.
Abbey Road reverb chamber. Note that it’s pretty gross and ventilation and plumbing runs through it. Where’s that dehumidifier?? Where’s Ringo?
In 1947, Bill Putnam put a speaker and microphones in a large bathroom at Universal Recording Studios. He fed some of the session he was working on (The Harmonicats Peg O My Heart) into the speaker, picked up the echoes and reflections bouncing around the bathroom with the microphones, and fed that back into his mix. Other studios followed and soon many studio complexes were converting storage rooms or adding on spaces to make a reverb chamber.
Reverb chambers sound somewhat like a concert hall, but much less natural because they’re typically much much smaller. In order to get a longer decay time, reverb chambers were treated to be very reflective, which resulted in longer decay times that are unnaturally bright and have a strange decay quality. Chambers sound like they’re decaying in sections. Think of “chunks” of reverb that get quieter over time, sort of like echoes, but reverb. To me, chamber reverbs have a “cannoning” sound to them — the reverb is thumpy.
Reverb/Echo chambers seem to have a cyclical, sort of “stop and start” decay curve. Visualize it this way:
Motown, the Beatles, everything coming out of Capitol Studios in Los Angeles, and just about everything recorded by a major studio through the 1950 into the early '70s, has reverb from a chamber on it.
Chambers sound lush and articulate, and are great for vocals and adding mood. They can sound big like a hall, but have better definition. A hint of a chamber on a part can add a tangible sense of space. A lot of chamber reverb sounds otherworldly and imparts a lot of mood.
Here’s a great example of chamber reverb: The Flamingos' I Only Have Eyes for You. This recording, done in 1959 live in the studio at Bell Sound Studios in NYC, is groundbreaking in so many ways: it’s one of the first times a record was produced to deliberately have a mood and not just be a documentation of a performance.
Reverb chambers, though, have problems. Often studios built them in basements, and that required constantly running dehumidifiers to keep them from filling up with water. And depending on the studio’s location, having a basically big empty room was stupid, from a real estate perspective. What studio in a major city can afford to pay for the square foot cost of a reverb chamber these days? As real estate prices went up, many chambers wound up converted into studios or office spaces.
Luckily, in the late 1950’s, some smaller solutions to the problem of reverb became available.
Plate Reverb
Plate reverb is luscious and rich. It’s very smooth, with a very even, almost linear decay. It’s the sound of vocals from the mid 1970's right up through now, but it is best used sparsely, to highlight elements of your mix. Too much everywhere makes a mess.
The guts of an EMT plate reverb.
Plate reverbs were usually made from a large plate of steel. A driver (basically a speaker) is screwed in somewhere around the center of the plate, and then two pickups (basically microphones) were screwed into the left and right sides of the plate (stereo!) towards the edges. Instead of the sound waves bouncing around a room, they bounce around the plate, and the result sounds like reverb. The decay time is controlled by damping the plate (imagine holding a huge pillow against it).
The first commercial plate reverb was developed by a German company, Elektromesstecknik. They released the EMT-140 in 1957. It was a monster—8 feet long and 600 pounds, and it wasn’t cheap.... but it was smaller than a reverb chamber and MUCH cheaper than building a room.
Plates became increasingly common through the 1960’s and into the '70s, and it wasn’t really until the advent of digital reverb units in the 1980’s that plate reverb began to fall out of favor. If a record was made from 1966 'til 1985, there’s a good chance there’s a real plate reverb on it.
Plate reverb sounds thick, lush, and has a very even decay time. The frequency response is similar to that of a chamber — a little unnaturally bright—but without the repetitive, segmented decay of a chamber.
Try to visualize a plate reverb in a way similar to this diagram: the reverb trails with energy distributed more or less evenly across its decay:
Plates are often used on vocals, especially lead vocals that need to pop out in the mix. When I was coming up through studios in the '80s and '90s it was common to put a plate reverb on the snare, even if the drums were cut in a big live room. The even decay and “thickness" of a plate reverb is very flattering.
Plate reverbs, too, have their problems. They are big and get in the way — even a small plate reverb is as big as a folding table on its side. You couldn’t have a plate reverb in a control room, not only because of its size, but also because it could start to feedback during the recording session! Studios put plates in the basement, or some other isolated room, and there had to be a remote control, yada yada, but it was sort of a pain in the ass anyway. Elektromesstecknik (EMT) developed the EMT-240, which was much smaller, and used a small piece of gold as a plate. About as big as a large PC, the EMT-240 didn’t require isolation to prevent feedback, and had a warmer character to its sound. Plates are mechanical, and mechanical things wear out and break, and once digital reverb units came onto the scene, plates faded. A few companies still make new plate units, but most of what is available today is either three decades old or a plug-in.
This record of Sister Golden Hair by America has a really nice, sparse use of plate reverb on it. Most of the recording is dry, but you can hear a lot of plate on the slide guitar and backing vocals, and just a touch of it on the lead vocals. This is an impeccable production, by George Martin, of a simply terrific song.
Spring Reverb
Spring reverb is bright and artificial sounding. It’s more of an effect than ambience. Top of the line spring reverbs can be quite beautiful sounding; cheaper units sound strange and “boingy.” When you don’t quite know what something needs, put a spring reverb on it.
The guts of a typical spring reverb.
Spring reverbs use a mechanical system similar to that used in a plate reverb, but instead of a big piece of steel, there are springs. A spring unit is smaller than a plate, and much cheaper, although really good studio quality spring reverb systems, like an AKG BX-20, were, and still are, pretty pricey.
Bell Labs originally patented the spring reverb as a way of simulating delays that would occur over telephone lines. The first musical application was in the 1930's, when spring reverbs began appearing in Hammond organs. Spring reverbs can be made cheap and small, and have been built into guitar amps since the 1950's. Spring reverb on a guitar is an utterly recognizable sound to the point of cliché.
Top quality spring reverbs, like the aforementioned AKG BX-20, are found in studios, but they didn’t replace plates, although they do have similar sonic qualities. An expensive, well-designed spring has a similar frequency response to a plate, but a more jumpy, inconsistent decay. Good spring reverbs impart a “halo” to an instrument. On a vocal, a spring doesn’t really sound like reverb, but rather, it sounds like an effect. I tend to think of spring reverb more as an effect than a means of adding ambience.
Amy Winehouse records used a lot of spring reverb sounds, to evoke a vintage, early 1960’s sort of vibe. I picked her recording of Round Midnight to give you a good example of a spring reverb on a voice. Notice the shimmering halo that surrounds the lead vocal— that’s a spring reverb. And listen for the level of the reverb changing during the mix, accentuating certain parts of the song.
Cheap spring reverbs sound boingy, but even that can be a useful effect. Rather than presenting some sort of cliché surf guitar as a reference for this sound, here’s a bit of madness from King Tubby. This is crazy stuff, with spring reverbs on drums and vocals, runaway tape delay all over the place, noises, distortion and slams, weird EQ’ing and filtering. If you’ve not listened to King Tubby.... jeez! Go listen to King Tubby!
We Have Reached the End of the Decay Time
So, some ideas, some patches, some tech stuff. I’ll cover what digital reverbs do in the future (really, what digital reverbs usually do is simulate all the reverbs I've described above). Remember, everything written above (except for the facts of how the various types of reverbs are constructed), is just a guideline. There are no commandments here. Use your ear, listen to recordings, and experiment.