How to Create Surreal Reverb Impulse Responses
Reverb allows adding the sound of ambient spaces—like a concert hall, room, or even a cathedral—to your recordings. There are two main types of reverbs. Algorithmic reverb models what happens to sound in an acoustic space, while convolution reverb loads an impulse (an audio file with the characteristics of a particular acoustic space, like a particular studio, cathedral, etc.), and imparts the characteristics of that “sample” on any audio going through it.
Loading white noise into a convolution reverb creates reverb effects, but the results—while “perfect”—usually aren’t very interesting. The Surreal Reverb Impulse Responses package of downloadable impulse responses gets its name because these are not impulses of conventional spaces, but of synthesized spaces created by shaping white noise with filtering, amplitude envelopes, comb filtering, reverse, and other effects. Without the constraints of a physical room, you can create all kinds of novel effects, as you can hear in the audio/video demo.
Many programs allow loading your own impulses, like PreSonus Open Air, Overloud TH3 (load as a cabinet IR), Waves IR-1, Native Instruments Reflektor, Ableton Convolution Reverb Pro, Cubase REVerence reverb, etc.. Although many convolution reverbs have a proprietary impulse format, most also import WAV or AIF files.
Start with a Noise Source
To make your own noise-based impulses, start by recording white noise from a synthesizer, noise generator like the signal generators in Cubase, Studio One, and Sound Forge, or search the web for free noise samples. I’d recommend normalizing the noise level to around -12 dB; some convolution reverbs don’t like impulses that use up all the available headroom.
Shape the Noise
Next, shape the noise into the amplitude and frequency response characteristics you want the reverb to adopt. For example, with a typical impulse, you’d want an amplitude decay as well as reduced highs as the impulse decays. Probably the easiest way to get creative is to load the noise into a track in your recording software, and automate changes or use various effects. You can also shape the sound with a synthesizer, or use audio editors like Sound Forge and Wavelab. You can create chopped reverb, as well as reverb that swells up and then disappears...or a super-bassy or ultra-thin reverb.
Of course, sometimes you want audio to sound like it’s in a real room, and a real room impulse is the solution. Noise reverb is more like a sound designer’s dream, the key to virtual reverbs, and a way to generate reverbs so smooth that they sound idealized. But one things for sure: you won’t be able to capture a room impulse that does what shaped noise can do, so experiment—you’ll have sounds no one else does.