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What Is Reverb? Exploring the Basics with Exponential Audio

by Geoff Manchester, iZotope Product Specialist April 3, 2019

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With Exponential Audio’s incredible reverb plug-ins now a part of the iZotope family, we thought it would be useful to do a quick primer on what reverb is and how to control it with Exponential Audio’s reverb tools.

What is reverb? 

Reverb is a series of many closely-spaced sound reflections—a ton of them—that we hear as a continuous sound. If you were to hear a room’s reverb slowed down by an extreme degree, you would hear the reflections as distinct repetitions of the original sound.

Those repeats would have variations in amplitude, frequency content, and envelope, caused by the physical properties of the room such as the dimensions of the space and what material it’s made from.

What does reverb do?

Reverb has many applications both in music and post-production. It can be added to individual mix elements in a song to create a sense of depth and space, or to connect instruments that were recorded in separate spaces by giving them shared acoustic properties. In the film and television industry, it is often used to ‘blend-in’ re-recorded dialogue by an actor after the filming process, through a workflow known as ADR mixing (Automated Dialogue Replacement) mixing.

Whatever the use case, reverb takes a dry audio signal and adds an acoustic environment to it that fools you into believing that it may have been recorded in a concert hall, stairwell or a space completely untethered to reality!

Below is a dry signal, a snare hit, and the same signal once it's been affected with reverb.

Before

After

Early Reflections

Early reflections are the first reflections to arrive at the microphone or listener. These help us localize a sound source and identify the size of a space. Small rooms will produce early reflections quite close together due to the proximity of surfaces. Large rooms will have early reflections that are spaced further apart due to the distance between surfaces.

In the audio clip below, the first snare hit is dry, but the second one includes early reflections from a hall reverb. Notice that they create an identifiable room sound even though there is no reverb, or late reflections.

Early Reflections Dry

Early Reflections Wet

Pre-Delay

Pre-delay is the amount of time between the direct sound and the start of the early reflections. Larger rooms naturally exhibit longer pre-delay because it takes longer for the direct sound to reach a surface and reflect off of it.

Listen to the following audio clip to hear a dry snare followed by its repeated ‘echo’ if you will. If you increase the pre-delay time, you hear a more pronounced gap between the dry audio and the start of the repeated sound. This can be used as a great creative reverb effect.

0 MS Pre Delay

100 MS Pre Delay

50 MS Pre Delay

600 MS Pre Delay

Decay Time (aka Reverb Time or RT60)

Decay time is the duration of time it takes for the sound pressure level in a room to fall by 60 dB. It might be helpful to think of this as a ‘reflectivity’ control. So if large and small rooms are constructed with the same materials, the large room will have a longer decay time. Although somewhat dependant on frequency, rooms with highly reflective surfaces such as concrete or hardwood will give longer decay times than rooms with absorptive surfaces such as carpet and fabric. The audio clip below contains a dry snare, then the snare with a room reverb set to around a 400 millisecond decay time, then the same reverb with around a 2 second decay time and a 4 second decay time.

No Decay

2 Second Decay

0.400 Second Decay

4 Second Decay

Damping

Damping is the absorption of high frequencies in the reverberation. Low damping values yield less high-frequency absorption, whereas high damping values produce more absorption of high frequencies. Lower the damping for a brighter reverb in which the high frequencies decay for longer or raise the damping to choke the high frequencies.

Listen to the following audio to hear a reverb with low damping followed by the same reverb with high damping. Notice the difference in the high frequency content.

Light Damping Factor

Dark Damping Factor

Types of Reverb

Finally there are many reverb types like Plate, Chamber, Hall, all of which are included in Exponential Audio’s reverb plug-ins

Hall

This is reverb resulting from the unique physical characteristics of concert halls, which are typically large spaces acoustically designed for a long, smooth decay. Acoustically, this means fairly long propagation times and slow reverb buildup. It also allows reverberation of long wavelengths, with a typically robust low frequency component.  

Pro Tip: Because of its long propagation time, a hall is seldom used on percussion instruments. The first 'bounces' of a strong transient are quite audible and are usually very distracting.  A plate or chamber reverb is more suited for percussion sound sources.

Hall Piano Dry

Hall Piano Wet

Chamber

Chamber reverb is reverb resulting from the unique physical characteristics of reverb chambers, which are reflective spaces such as a corridor or stairwell designed to house a speaker and microphone configuration for triggering and recording the reverb.

Chamber Dry

Chamber Wet

Plate

Plate reverb is reverb resulting from a vibrating metal plate. In a real plate reverb, a large sheet of metal is suspended in an enclosure. Multiple transducers—a small driver and at least one small contact microphone or pickup—are attached to the plate. Dry signal is sent from a console or audio interface to the driver, which causes the plate to vibrate. The contact microphone picks up these vibrations and outputs them for use in the mixing system. The larger the plate and the further apart the transducers, the longer the reverb time.

Plate Dry

Plate Wet

Conclusion

In conclusion, take some time to dive into tweaking your reverbs. Experiment with pre-delay and try printing reverb in reverse, or combine multiple reverb types. Chances are you'll probably unlock some extra sonic goodness. Try reverb in mono, stereo, even surround since Exponential Audio’s reverb plug-ins go from 5.1 to a whopping 22.2 channels!

Hopefully you’re now a little more familiar with what reverb is and how to best manipulate it to suit your post or music production needs. Take care!

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