Join Alex U. Case for an in-depth discussion in this video The anatomy of reverberation, part of Foundations of Audio: Reverb.
At first, I think we all have a pretty intuitive reaction to reverb. The unique reverberant signatures of concert halls and cathedrals, stadiums and stairwells, are noticed by almost everyone, not just audio enthusiasts like us. Kids clap in caves, sing in showers, holler in halls, and shout at subway stops. This intuitive flirtation with reverb is very much driven by the unmissable sonic reaction of the space to the sounds we make.
While a child plays with reverb without much thought, making musical use of the effect is the much more daunting challenge presented to us every time we record. It's a tough concept to truly master. To describe reverb we need a set of parameters, and we need to assign them some values. But let me warn you ahead of time trying to describe something as ornate and expressive as reverb with just a few numbers is clumsy. The numbers will never fully define a reverb. Imagine trying to describe the sound of your favorite piano, the tone of your favorite vocal microphone, or the flavors in your favorite fish taco, using numbers only.
In the end, our understanding of any given reverb is always an aesthetic judgment, our own individual artistic assessment. Use the parameters as guides, but as always listen carefully and be opinionated. Go for what you like, never mind the details. One way to gain insight into reverb is to look at how it reacts to a specific test signal known as an impulse. An impulse is the shortest of clicks, a simple wave shape that snaps up and immediately snaps back down to silence, short and simple.
Play an impulse in a room, record the result, and you've captured the room's impulse response shown here. It consists of three key components, landmarks really. First is the direct sound, that's the original impulse itself. This is followed by some visible spikes of early energy which are known early reflections. This in turn is followed by a dense wash of decaying energy. This is the much more complicated energy coming from the later reflections in the room, this is the reverb tail.
Dividing your thinking into these building blocks can help even as we play music tracks instead of impulses. The direct sound is your original, likely close to mic to track, the kick, the snare, the vocal, the bass trombone. It's the dry part of the mix. As we had reverb to these tracks, we are adding a complex kind of sustain that includes the early reflections and the reverb tail. We will sometimes focus on the properties of the early reflections and other times focus on the reverb tail, each has sound qualities we need to get under control as we record and mix.
With these three components of reverb in mind, we are ready to look at the most important adjustable parameters in our reverb devices, the knobs we turn, the buttons we press, and the sliders we push, as we add reverb to our music.
These techniques can be practiced with the free Get in the Mix sessions, currently available for Pro Tools and Logic Pro.
- What is reverb?
- Understanding how acoustic reverb works in rooms
- Working with the signal flow, effects loops, and available CPU resources
- Understanding core parameters, like reverb time and pre-delay
- Simulating space
- Creating nonlinear reverb
- Building pre-delay effects
- Using reverse reverb
- Using convolution correctly