Reverb is the original effect: the sound of the music interacting with the space in which it’s played.
Sound moves fast—over 1000 ft/second. But that’s slow enough that we can perceive the difference between soundwaves that come directly to our ear, and soundwaves that are reflected first.
Your ear is hearing the original sound, plus the original sound after it’s bounced off the walls of whatever studio, concert hall, cathedral, cave, bathroom, or parking garage you’re in.
Originally, reverb was achieved naturally, by putting the musicians in a “live” room—one with plenty of hard surfaces for sound to bounce off on its way to the microphones.
Since the size & reflectiveness of a room aren’t things you can easily adjust, recording engineers began building “echo chambers” to get reverb.
Starting with a “dry” recording made in a “dead” room, they could put a speaker in one corner of a live room & a microphone in the other and record the sound of the music interacting with the room.
From there it was a matter of simply blending the original dry recording and the “wet” signal together to get the desired effect.
Still, that’s kind of a pain in the ass.
Springs & Plates
In his book How Music Works, David Byrne makes an interesting point about how the venue where we play the music shapes the music itself.
Since people were accustomed to hearing organs in large church spaces, in the 30s organ maker Hammond invented the spring reverb to give its home instruments that same sense of space.
A transducer (sort of like a speaker) sends audio vibrations down a metal spring. On the other end is a pickup not unlike the ones on your guitar. The spring “stores” vibrations, dispersing their arrival at the pickup over milliseconds… much like soundwaves bouncing around a room en route to your ear.
In the late 50s, German company EMT invented the plate reverb. It’s the same idea as a spring reverb, only using a huge (~4’x8′ and ~500lbs) sheet of metal.
Plate reverbs were a huge paradigm shift for studios: more useful for music production, offering much greater control, and taking up a tiny fraction of the space needed for an echo chamber or large live room.
In the 60s, Hammond designed an improved spring reverb that was small enough to fit inside a guitar amplifier. Fender licensed it, and the popularity of their amps cemented it in our perception of what electric guitar sounds like.
Reverb Goes Digital
But wait, there’s more!
In the late 70s we saw the first digital reverbs from companies like EMT and Lexicon. These units multiplied the original signal, added slight delays to the copies, and recombined them to recreate the sensation of natural reverb in a room or echo chamber. The math behind what gets delayed & how much is known as a “reverb algorithm.”
In the late 90s, Sony turned this paradigm on its head—why create an algorithm from scratch? Why not capture the reverb of an existing physical space?
They called this approach “convolution reverb” and it remains popular today.
For example, when the Chicago Symphony Orchestra performs outdoors at the Pritzker Pavilion, the sound system there uses a reverb algorithm painstakingly modeled off their concert hall space a few blocks away.
Currently we’re seeing more experimental reverbs that do things that aren’t modeled on natural sounds. Of these, probably the only two you need to know about are modulated reverb and shimmer reverb.
Modulated Reverb takes the wet signal and runs it through a modulation effect like chorus or phaser.
Shimmer Reverb takes the wet signal and adds an pitch shift (usually an octave up).
What Do All These Knobs Do?
mix — controls the balance between the wet and the dry sounds
decay — controls how long sound reverberates. you can also think of it as controlling how large the room/spring/plate is
predelay — controls how soon the reverb starts after the initial sound. set it too low and your dry signal can get lost in the wet. set it too high and it’ll sound like a slapback echo.
modulation — controls how much chorus, phaser, vibrato, flanger, etc is added to the wet signal
high filter/low pass/high damping — controls how much high end gets EQ’d out of the wet signal (helps keep big reverbs from getting really washy and indistinct)
low filter/high pass/low damping — controls how much low end gets EQ’d out of the wet signal (helps keep big reverbs from getting muddy)
(sound demos coming just as soon as I finish setting up my new office!)