Reverb is one of the most important effects you’ll use in music production.
Alongside compression and EQ, you’ll probably reach for a reverb plugin during each and every mix.
But why exactly is reverb so crucial? What makes a great reverb plugin, and how can you use them intelligently to get the best possible results?
To use reverb like an expert, you need to understand how it works and why it’s important in modern mixing.
In this article, I’ll lay out the beginner’s guide to reverb in music production, break down the essential types of reverb and outline key mix situations to help you understand how to use it.
Let’s get started.
What is reverb?
Reverb is an audio effect that simulates the acoustic reflections that occur when a sound is heard in the physical environment.
Ambience is an essential characteristic of the sounds that we perceive in day-to-day life. Since we’re usually situated inside enclosed spaces that have distinctive reverberation properties, our physical environment plays a significant role in shaping the sounds we hear.
The qualities of a space’s reverb give our brains important cues for determining the direction and distance of a sound’s origin from the listener.
In mixing, reverb is a fundamental technique for enhancing the realism and immersion of a studio recording. It does this by helping to situate a sound within the virtual space of the mix.
Reverb may be provided naturally by mic’ing sound sources from a distance, but more commonly it is created artificially using plugins, hardware devices or other methods.
Why is reverb used in mixing?
The use of artificial reverb in music production dates back to the earliest developments in studio technology at the dawn of the LP era.
Early recording engineers quickly learned that capturing too much ambience during recording led to less flexibility in the mixing process.
After all, once you’ve recorded your sources at a distance with ample natural reverberation, there’s no way to reduce the ambience in the finished recording to get a stronger direct sound.
On top of that, engineers found that while rich ambience was often flattering to the sound in isolation, it reduced the overall clarity when many instruments were blended together.
As studio design matured, recording environments were built to give engineers more control over the room sound in their recordings.
Over time, close mic’ing techniques and dry, controlled environments became the norm for recording studios.
But despite the gains in clarity, something was missing to make the final results feel natural.
Engineers needed a way to add ambience after recording had taken place. And they needed it to have predictable qualities that would enhance the sound, while still reaping the benefits of close mic’ing.
Reverb basics
The earliest devices that produced artificial reverb were electromechanical. These approaches approximated the reflections of sound waves off hard surfaces by sending electrical signals through different mediums.
First springs and then giant metal plates, these classic techniques found a home in the language of music production and are still in use today.
But for the majority of tasks that require studio reverb, digital tools are the most widely used in the modern era.
The first digital reverbs were based on simple delay lines. If you imagine a sound wave emanating from a source within an acoustic environment, you can think of the first reflection off the walls like an echo.
When a sound wave interacts with a hard surface, its reflection bounces off and comes back toward the source after a short delay, with a slightly different sound.
Maybe the surface absorbs a bit of the high end, or some frequencies cancel out when they combine back with the original source.
In the real world, sound emanates in many different directions, interacting with many different surfaces before combining back in unpredictable ways.
Not only that, these reflections don’t just beam directly back toward the source, they reflect off other surfaces, producing reflections of reflections.
Algorithmic reverb
Clever DSP engineers use multiple delay lines tapped at different intervals with networks of filters and feedback to approximate the journey of a sound as it bounces around a space.
Since the input signal follows a series of repeatable steps to arrive at the result, this approach is called Algorithmic Reverb.
Like the spring and plate reverbs before it, algorithmic reverb techniques gave rise to beloved production tools with unique character that became popular in music production.
There are many still offered today, including a modern take on the classic style from our friends over at Baby Audio.
But ultimately, algorithmic approaches could never quite model real life down to the last detail.
After all, the interactions of a sound wave in physical space are phenomenally complex, especially when your only tool to approximate them is a humble delay line.
Enter the next development in reverb, convolution.
Convolution reverb
Convolution sounds like a…convoluted term, but the idea is straightforward when it comes to reverb.
If the reverberation inside a pleasing acoustic space like a concert hall or cathedral is the response to excitation by a sound wave, it should be possible to emulate the whole process.
The trick is to use a unique signal called an impulse. An impulse is a theoretical signal with exacting properties—equal energy at all frequencies, a duration of only a single sample and amplitude at full scale.
Since the impulse signal is so clearly defined, it can act like a photographic negative when compared against the impulse response of an acoustic space.
Let me explain.
Imagine you set up microphones all around a world-famous concert hall. Then you place a loudspeaker at the conductor’s position and play an impulse signal. The recording you make of the reverberation that follows is the response to the known qualities of the impulse signal.
All you have to do is remove the sonic signature of the impulse, and then you can apply the resulting profile to any sound.
Convolution is the technology that makes it possible. Technically speaking, it’s a complex mathematical process that maps the properties of one signal onto another, but the upshot is that you only need to record a space once to load the IR profile into a reverb plugin and simulate the response with any input material.
Convolution comes with distinct benefits for realism, but it’s inherently less flexible than algorithmic approaches.
If you want a 40 second decay with an algorithmic reverb, you can just set the delay lines long enough to create it.
But in a convolution reverb, you can’t easily produce an equivalent impulse response that works as you'd expect.
On the other hand, convolution reverbs can easily take you to real physical locations known for their acoustic properties.
Want to hear the reverb from a famous opera house or recording studio? Chances are someone has created an IR file you can load into any convolution reverb.
There are even IR captures of hardware algorithmic reverb units if you want to take the idea to the extremes.
There are many more pros and cons to consider, so if you want to see a more detailed overview of the two techniques, head over to this post on the Baby Audio blog.
Convolution vs. Algorithmic vs…alternatives?
So which reverb type should you use?
Here’s the rule of thumb. Reach for algorithmic reverb when you’re looking for sound design, enormously long reverbs or classic sound that emulates earlier approaches to reverb.
Choose convolution if you’re looking for realism, especially if you have a specific space in mind you want to emulate.
But If you’re somewhere in the middle, there are alternatives to the two main approaches that you should consider.
We built Perfect Room 2 to harness the best of both worlds and its unique technology is neither algorithmic nor conventional convolution either.
Instead of starting with a set of delay lines or an IR capture of a physical space, Perfect Room 2 creates a Dynamic Room Response profile based on a mathematically ideal acoustic environment.
The Dynamic Room Response engine
So why did we develop a fresh approach to artificial reverberation with Perfect Room 2?
If you’ve used either of the two reverb types I’ve described so far, you might be familiar with some of their drawbacks.
Algorithmic reverbs will always have some basic characteristics that arise from their network of delay lines.
Since each delay begins as a complete copy of the original signal, it can only be filtered subtractively as the reverb decay progresses.
That means that some frequencies will naturally build up in the reverb tail and reinforce areas that may already be sticking out in the original
Not only that, algorithmic reverbs tend to have a noticeable concentration of density around the initial phase of the decay since the first reflections are the most similar to an unfiltered delay.
Over time, engineers developed clever techniques to mitigate these issues. But there’s no way to eliminate them completely, since they’re artifacts of the process itself.
Similarly, typical convolution comes with all the drawbacks of the physical spaces used for the IR.
The real world is messy. Though many spaces have pleasing acoustic qualities, they may also bring their own baggage to your sound.
For example, capturing a stereo IR file will inevitably create some tradeoffs in the information between the left and right channels.
Since the IR was captured in physical space, the left and right channels will always be somewhat correlated, which can lead to cancellation when the two are combined.
If you’re going for realism, this is a good thing! But you certainly don’t want to introduce phase issues on your entire mix during say…mastering.
Clean and transparent reverb
Where these issues matter most are mix situations in which clarity, transparency and fidelity to the source are essential.
I mentioned the mastering example above, but there are plenty of others.
Critical acoustic recordings, full mixes and other demanding applications call for reverb that doesn’t alter the original sound in a negative way.
That’s what we built with Perfect Room 2.
Its unique engine design ensures you start with a neutral response. From there, the rest is up to you.
In true Denise fashion, we added the controls we’d like to see on a great creative reverb, even one designed for a clean overall character.
If you’ve ever wished for a reverb plugin that gives you back exactly what you put in, you’ll love working with Perfect Room 2.
Mix applications for reverb
Reverb isn’t just meant to make things sound further away.
It plays an important role in making a mix sound glued and cohesive and helps convey the sense that each instrument occupies its own defined space.
In the Perfect Room 2 mix demo, Michael breaks down how Perfect Room 2 offers unique benefits in four key situations:
- Extending ambience for sources with complex transients
- Adding stereo width to a mono instrument without phase issues
- Creating rich reverb to enhance the blend of lead and background vocals
- Adding top end air to a full mix.
And that’s just a small slice of what’s possible with Perfect Room 2!
There’s a free trial available so the best way to experience its clean and transparent character is to test it out in your own mixes.
Now that you know the basics of reverb, download the free trial today from https://www.deniseaudio.com/plugins/perfect-room-2 to get started with Perfect Room 2.