Reflecting on Reverb: What It Is and How to Use It

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Perhaps you’re neck deep in reverb as you read this. Maybe you’ve been using reverb plug-ins and pedals for years or there’s a chance you shy away from them, acting upon the advice of wise sages. As humans, we listen to reverb throughout our lives, often joyously unaware or against our will. If at some point in your existence on Earth, you found yourself in a bathroom, you heard some reverb.

As musicians and audio engineers, we regularly add reverb, sometimes not knowing much about it. What follows is a primer on what’s really going on with reverb.

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 repeats 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 dimensions of the space and what material it’s made from.

We normally aren’t able to hear those as distinct repeats because there is so little time between them. Two similar sounds spaced apart more than about 35 milliseconds can be heard and identified as two separate sounds. However, we perceive those same two signals as one blended sound if they are less than 35 milliseconds apart. Thirty-five milliseconds equates to about 40 feet (a round-trip reflection in a 20-foot room).

Listen to the audio clip below to hear a dry snare, a snare with two reflections 50 milliseconds and 100 milliseconds apart (panned hard left and right), then a snare with two reflections 15 milliseconds and 30 milliseconds apart (panned hard left and right). Notice that the first snare hit is totally dry, but the second one has audible “echoes” from the reflections. However, even though the third snare is combined with reflections, you can’t hear them as separate, distinct echoes, though they do seem to impart a sense of space.

Elements of reverb

In the analog world and in digital simulations, reverb is defined by several key elements, and modification of these elements can drastically change the sound of the reverb.

Early Reflections: 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.

Pre-Delay: 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 the snare with room reverb (with no pre-delay), then the snare with the same reverb and 100 milliseconds of pre-delay. Notice the gap between the third snare hit and its reverb.

Decay Time (a.k.a. Reverb Time or RT60): the duration of time it takes for the sound pressure level in a room to fall by 60 dB. 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 a 400 millisecond decay time, then the same reverb with a 2 second decay time.

Diffusion: the dispersion and density of reflections. Low values result in low reflection density and increased audibility of individual reflections, while high values result in an increased reflection density and a more uniform wash of reverb. Use high diffusion for a smooth reverb or low diffusion for a more “chattery” reverb.

In the following audio example, the first snare hit features a room sound with low diffusion (notice the “chatter”), while the second snare hit has the same room sound with high diffusion (notice the smoothness).

Damping: 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.

It’s likely that you’ve seen those settings many times before, probably on reverb plug-ins, pedals, and rack units. So, does that mean that two reverbs with the same settings will be the same? Decidedly not! Two different types of reverb with the same user-adjustable parameters will not sound the same.

What are the types of reverb? Step this way, please.

Types of reverb

Reverb types are various methods by which reverb is created. They’re extremely common; get to know them! Following the description of each reverb type is an audio example of that reverb. No direct signal is included, so you can focus on the reverb.

The first three clips are simulations of acoustic environments. The characteristics of the reverb will conform to the expected behavior in our physical universe. The second two clips are mechanically produced, and do not necessarily seek to sound realistic. Plate reverbs, for instance, do not have a high frequency rolloff built in—therefore they sound brighter. They also do not have spaced reflections that vary, so they are more diffuse sounding.

Hall: reverb resulting from the unique physical characteristics of concert halls, which are typically large spaces acoustically designed for a long, smooth decay.

Room: reverb resulting from the unique physical characteristics of rooms such as studios or living rooms, which are typically smaller than halls and are designed for shorter decay times.

Chamber: 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.

Plate: 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.

nectar2-reverb2

Nectar 2’s reverb, modeled after the iconic EMT 140 plate reverb

Spring: reverb resulting from small vibrating springs. Like plate reverbs, spring reverb units rely on vibrations to create reverb. Dry signal is routed to a transducer, which is attached to one end of multiple springs. Signal passing through that transducer causes the springs to vibrate. Those vibrations are picked up by another transducer on the other end of the springs. The longer the springs, the longer the reverb time.

Halls, rooms, and chambers will have a three-dimensional quality due to the three dimensions in which sound can reflect (in those spaces). Plates and springs will exhibit a two-dimensional character as a result of the vibrational mechanics of the physical plate and springs.

Using natural analog reverb

The natural reverb in a bathroom, concert hall, or studio environment can be used to augment your dry tracks. Although doing so is far more laborious than tossing a plug-in on a track, it can give you unique reverb unobtainable with your software or hardware reverbs. The following steps outline the process of using natural reverb in the mixing process.

1. Find a (preferably quiet) room or space that has an interesting reverb.

2. Go to that place with your computer, audio interface, one or two speakers (for mono or stereo playback), one or two microphones (for mono or stereo recording) and stands, and all necessary cabling. (speaker quality will affect the results of course)

3. Connect your speaker(s) to your audio interface, preferably to outputs other than your main mix outputs.

4. Set up the microphone(s) if recording in stereo, preferably using a stereo miking technique that does a good job portraying the stereo field in the room and connect them to your audio interface.

5. Create a new mono or stereo audio track (depending on how many mics you use). Set its input to receive the mic(s). Make sure that the output does not feed your speakers; you do not want the hurting that a feedback loop would put on you!

6. Use an auxiliary (aux) send to route the dry signal to the speaker(s).

7. Adjust your mic preamp levels and listen to the reverb.

8. If desired, move the speakers and/or microphones to capture the room differently (tweak gain as needed).

9. Record the reverb to the new track.

10. Enjoy!

Note: It’s a smart idea to create an aux track to control your reverb, as opposed to placing the reverb directly on your instrument track. Why? If you want to use this reverb on multiple instruments, you can just create a bus on the track and send them to the aux, giving you more control over your mix and saving valuable CPU.

Using artificial digital reverb

An easier and more flexible way to add reverb is to use digital hardware reverbs or reverb plug-ins. There are two primary types of digital reverb—algorithmic and convolution.

Algorithmic Reverb: reverb simulated through mathematical calculations (an algorithm). Algorithmic reverbs may attempt to imitate the sound of real rooms and equipment or create reverbs that don’t exist outside of the digital realm. Examples of algorithmic reverbs include the venerable Lexicon reverbs, TC Electronics, Exponential Audio’s PhoenixVerb, Sonnox Oxford Reverb, and Valhalla DSP’s Valhalla Room, just to name a few of the many.

Convolution Reverb (a.k.a. IR or Sampling Reverb): reverb created through processing an impulse response (IR), which is a recording of a signal that was played in an actual room or sent through a piece of gear. The signal typically either contains all frequencies or is swept across all frequencies, allowing analysis of how the room or gear affects the signal over time. Examples of convolution reverbs include Audio Ease AltiVerb 7 and HOFA IQ-Reverb, though there are many more. When compared to algorithmic reverbs, they are incredibly flexible and deliver more varied reproductions of real rooms and equipment, but require substantially increased CPU resources and involve more latency (they are basically sample players).

iZotope’s Nectar 2 combines algorithmic and convolution reverbs, taking the best of both worlds. As explained in the Nectar 2 help documentation:

“Rather than just use pure convolution, we’ve used a hybrid DSP algorithm which utilizes both convolution and algorithmic methods of generating reverb. Convolution is used to accurately generate the early reflections of the plate while an algorithm has been written to synthetically generate the late tails of the reverb. Using this sort of hybrid DSP provides continuous control of parameters like the damping in real-time, which isn’t possible with pure convolution. Additionally, this hybrid DSP is significantly more CPU efficient than pure convolution.”

The following audio clip toggles between algorithmic and convolution reverbs without dry signal. The first snare hit is through an algorithmic reverb, while the second one is through a convolution reverb. Then the loop toggles bar by bar between the two reverbs (algorithmic/convolution/algorithmic/convolution/algorithmic/convolution). Both reverbs were from the same plug-in manufacturer and were configured to the same settings (where possible).

There are a couple of special reverb effects worthy of mention—reverse and gated.

Reverse reverb is reverb in reverse (a fun technique to try on vocals and drums!). Rather than a splash of reverb decaying to nothing, it starts at nothing, then ramps up to an abrupt end. Listen to the next clip for an example!

Gated reverb is a non-linear reverb. Rather than decaying smoothly into silence, its tail is attenuated swiftly by a noise gate. The result is often a short, explosive sound, as heard in the next audio clip. It’s useful for elongating percussive sounds, which increases their audibility without having to turn them up.

Choosing the right reverb

With so many options, how do you go about selecting the best type of reverb? Well, that’s a tough one. One reverb will never be the best one for everything. A reverb that you swear by for vocals may be terrible on drums. A reverb that normally slays on drums isn’t going to be ideal for drums and for all clients. Although choosing reverb is a subjective process, there are some solid points to start from. The following clips allow you to hear examples of appropriate and not quite ideal reverbs on various sources.

Note: too many reverbs occurring simultaneously will usually make a mix muddy—and it will be hard to hear each reverb effect.

Drums: wood room then spring reverb

Pro tip: watch out for too much low-frequency energy (below 100 Hz) in your drum reverb; it gets boomy fast and usually doesn't sound good!

Vocals: plate then hall

Pro tip: make sure you don't have too much high-frequency information in your vocal reverb, unless you want the sibilance to excite the reverb. You can roll off high frequencies in the aux send or roll off high end in the reverb itself.

Strings: hall then gated

Electric Guitar: spring then large room

Conclusion

If you allocate some time to dive into tweaking your reverbs, you’ll probably unlock some extra sonic goodness. Try them in mono, stereo, and experiment with extreme settings when you aren’t busy. Also, keep your ears open for interesting natural reverberation as your go about life!