It’s probably the most commonly used effect of all, but just what is reverb?
If you’re a producer, home recordist or guitarist, you’ll no doubt have used reverb effects at some point. If you haven’t, you’ll almost certainly be aware of what it sounds like.
Reverb (short for reverberation) is one of the oldest of all audio effects, and aims to recreate the natural ambience of real rooms and spaces. Adding a softer edge and a sense of ‘space’ to sounds, it is an essential tool when mixing a track, and commonly a bedrock of many guitarists’ pedal boards.
Even if you’re familiar with its sound, you still might ask, just what is reverb?
Well, here we answer that question…
A quick science lesson (no, don’t run away!)
To understand what reverb is, its important to understand the acoustic phenomenon it aims to recreate. To understand this, you need to understand the science that causes it. Don’t panic, though- it’s very simple, and very useful to understand.
Put simply, reverb is the effect of sound being reflected back to a listener’s ears from surrounding objects.
Picture this example- you’re out for a walk in the country, and on the way you end up at the bottom of a wide valley surrounded by hills. You can’t miss an opportunity like this, so you shout ‘echo!’ at the top of your lungs. A fraction of a second later, you hear it repeated back to you.
Essentially, what is happening here is that the sound is leaving your mouth at approximately 340 metres per second, travelling through the air until it reaches the valley walls, then bouncing back towards you the listener.
As this takes a certain amount of time (if the valley wall is 170m away, it will take 1 second to return), there is perceived delay between your shout and the reflection, causing the echo effect.
With me so far?
Because the valley is (aside from the walls) pretty much an open field – that is, there are no other hard objects to reflect sound back- the echo is the only reflection you hear.
Things are more complicated in enclosed spaces, however…
Rooms, chambers and enclosed spaces
If a sound is made within an enclosed space, such as room, hall, cathedral, cave, or whatever, the principles or sound reflection are much the same.
However, as you are surrounded by hard, reflective surfaces, and the surfaces are far closer, the delayed, echo effect is rarely perceptible, and the number and pattern of reflections is far more complex.
To explain how this works, image an oblong shaped room with hard walls, similar to the diagram below, with a willing subject ready to make some noise within.
When our subject makes a noise, it will travel in all directions from the source at the same speed. When it does, it reaches the walls closest to it first, and is reflected back to the listener the soonest.
These are known as early reflections. The delay time between the source sound and these early reflections is known as pre-delay, and is the main factor that dictates how ‘big’ a reverb is perceived to be.
The longer the delay, the further the sound has to travel, so the bigger the space must be. Going back to our valley example, the distance there is so big that it is heard as entirely separate sound. Simple, eh?
After this phase, the reflections from elsewhere in the space (of which there are far more), which have been bouncing around the other walls and hard surfaces, start to return to the listener.
The shorter the distance these have travelled, the sooner they will arrive, and the louder they will be. Conversely, the further they have travelled, the later and quieter they will be.
As these many, many reflections are arriving at fractionally different times, the effect is of a gradually decaying sound, known as reverberation.
The length and character of this decay is affected by many factors, such as room size, shape, number of hard surfaces, and the materials that these are made of. So a big Cathedral should have a long pre-delay, and a long decay, due to its size, shape and construction, whilst, say, your living room will most likely be a far shorter delay and decay.
As previously stated, reverb effects for musical use have been around for some time. As early as the ‘50s, plate reverbs were used to simulate natural acoustic reverb. These worked by using a transducer (a speaker) to send the source sound through a piece of sheet metal, with another transducer (a microphone) to pickup the resulting the decayed sound.
To increase the pre-delay (and perceived space), a delay would have to be added into the reverb channel.
The effect was surprisingly, er… effective, though. However, with plates often huge and heavy. For example, the famous EMT 140 weighed a whopping 270kg.
Still, it was more practical that using a reverb chamber- a room designed specifically to created reverbs. Here, a speaker would be set up in the chamber, with microphones elsewhere in the room, such that sounds could have natural reverb added.
A spring reverb is much like a plate reverb, except it swaps a huge and heavy plate of metal for a far more practical spring. As a result of the smaller size, spring reverbs were introduced to many guitar amps, and still feature on many today.
When digital technology became more commonplace in music gear during the eighties, digital reverbs represented some of the most welcome uses of it.
Rather than employing physical means to generate reverb decays, these use computer chips and mathematical algorithms to calculate the audible effects of reverb. The advantages of these are huge. They can be switched to emulate different acoustic spaces, or reverb types easily (most will offer room, hall and plate settings as standard).
Many even offer the ability to get into the ‘nitty gritty’, and control pre-delay time, number of early reflections, decay time, decay character and more.
Though the classic studio reverbs by Lexicon and the like have become less commonplace, there are many classic guitar reverbs available. Check out the EHX Holy Grail Nano, Boss RV-5 and TC-Electronic Arena reverb.
Convolution reverbs are recent development of digital reverbs. These are usually software plug-ins, and harness the incredible CPU power now available to accurately model the sonic character of real acoustic spaces.
So, an engineer will head out with a measuring mic and a computer to, say, a cathedral, and ‘sample’ the space, creating impulse responses.
As a result, users can create their own reverb types fairly easily on many available convolution reverbs.
So there we are- ‘what is reverb’ explained. But, what is it used for?
In the studio, it is used to create a sense of space and depth in a mix. Sounds that have a lot of reverb seem further away, whilst dry sounds seem closer and more intimate. In addition, recorded sounds that are completely dry can sound a little bit unnatural.
Reverb is also used as an atmospheric effect- sounds that have big, spacious reverbs can suggest the ‘drama’ of the spaces they emulate, for example.
Here’s a few audio examples…
View a complete range of reverb pedals on the Dawsons Website.