Reverb is the effect a sound makes when produced in a given space. Clap your hands and listen to the sound of the room as that clap reverberates off the walls and ceiling. Clap your hands in a different space, say a church, and you get a very different kind of reverb — longer, louder, brighter. The nature of any reverb is determined by many things, including how far away the wall and ceiling surfaces are, what they’re made of, whether there’s carpet and more. More recently, a new form of reverb is taking hold: convolution reverb. This was initially very expensive and niche, but it’s now available to all, thanks to affordable plug-ins like Altiverb, Waves IR-1 and Pristine Space, and even freeware such as SIR1.
Convolution reverb isn’t a simulation of a real space, it is the real space. Just as a musical sampler or wavetable synth uses recordings of real instruments for its sounds, convolution reverb uses real reverbs. It calls these impulse response files. An impulse file is simply a recording of a short, sharp noise, followed by the reverb it’s produced, saved as a regular .wav file. This noise could be anything, but usually an electrical spark or loud clap is used. Load an impulse file into a convolution reverb (also called a convolver) and the properties of this reverb will be applied to any sound you pump through it. You don’t have to do a thing, aside from determine the balance of Wet and Dry.
While a modern digital reverb is still useful for creating unusual sounds, if you need to create a specific environment, convolution reverb is the answer. This is vital in sound design for film and TV, such as when blending location sound with ADR (dialogue rerecorded in a studio). You can also create unusual convolution reverbs by simply loading any .wav file you like or using a dedicated IR creation tool like Voxengo Impulse Modeler (http://www.voxengo.com/product/imodeler) to create spaces that are realistic yet impossible to record, like the interior of a spaceship.
There are lots of impulse files you can use in your convolution reverb, such as:
- Noisevault: http://noisevault.com/index.php?page=ir-library
- echochamber: http://www.echochamber.ch
- Voxengo: www.voxengo.com/impulses and www.voxengo.com/product/pspace
- Samplicity: http://www.samplicity.com/bricasti-m7-impulse-responses/
Add reverb to your audio with SIR1
Here we'll show you to add convolution reverb to your audio using the freeware plug-in SIR1. Note that this and other convolvers are audio plug-ins that require a host application like Cubase, SONAR, Vegas, or any video or audio tool that supports VST plug-ins. Also note that SIR1 may crash in 64-bit hosts, although the SIR2 commercial update (http://www.knufinke.de/sir/sir2.php) supports 64-bit hosts and has many other advanced features.
- Download SIR1 from http://www.knufinke.de/sir/sir1.php. Alternatively, you'll find SIR1 on PC User's May 2011 cover disc, as well as several free impulse files. Install SIR1 copying the .dll file to the VST plug-ins folder of your host application; for example, C:\Program Files\Cakewalk\Vstplugins for SONAR. There can be multiple VST plug-in folders and most host applications will let you scan all of them for any plug-ins, so check your host’s preferences. You can also unpack the IR samples here. Put them all in the same folder.
- Create a track in your host software with some audio you want to apply the reverb to. You apply SIR or any other convolution reverb just as you would any other VST effect. Click the ‘Open File’ button then browse to where you saved the IR files. Click any one of these files and the entire folder of .wav files will be displayed within SIR.
- Clicking on any one of the loaded IR files will make that the current reverb. Play your host’s sequence and adjust the Dry and Wet sliders to control how much reverb is applied. You can alter other properties including a bit of EQ, but if you simply want the original reverb as it was recorded, you don’t have to do anything more.
