What Is Convolution Reverb?

Convolution Reverb is one of those magical tools that most post-production sound engineers and sound designers rely on. It allows you to take a recording of any space and apply its acoustical properties to any other sound you want. Pretty amazing, right?!

Once upon a time, before digital computing power was up to snuff, the only way to make a sound mesh seamlessly with sounds recorded in another space was through a process called ‘worldization’ (invented by Walter Murch on the film American Graffiti). This involved taking the target sound and playing it through a speaker in the actual room, re-recording it, then later replacing the original, or mixing it in along with it.

 

How Convolution Reverbs Work

To blend one sound with the acoustic properties of another, the software needs something called an ‘Impulse Response’ (IR), which is a recording of a short, loud sound, like a clap or a generated frequency sweep (from 20Hz-20kHz) taken in the room of choice. The recording will contain the clap or sweep as well as the spatial reverb effects of that room.

With the impulse response recording in hand, the software does some mathematical wizardry to de-convolve (remove the original sound from) the signal to extract only the wet spatial details that you need.

Then all you have to do is throw it on a sound or a track and tweak some of the parameters to your liking. Often this can result in a very realistic reproduction of the space.

The software also gives you the ability to control the levels of the early reflections separately from the late reflections (as well as the ability to extend or shorten the length of the reverb), which is very important for tuning the effect properly.

For those of you who don’t understand how reverb works, reverb is the accumulation of all of the sound reflections in a space. Thousands of them are happening all the time and reverb software simulates those reflections. Early reflections are the reflections that bounce back to your ear first before the others, and can often have a very pronounced effect on the actual sound as it melds with it more closely. The late reflections form into what you commonly think of as reverb; the tail.

 

Ways To Use It

Room Matching

Using convolution reverb to make sounds match the acoustical properties of a space is likely its most common function, proving an invaluable tool for filmmakers to help better match Foley and ADR to the original space. If you plan to do this, remember that less is more. Dry studio ADR is better than ADR that sounds like it’s been placed in an artificial room. Play with it and tweak until you can thoroughly fool the audience.

Creative Effects

Nowadays, most of these software plugins will accept any old wav/aiff file as an input. This means you could trick the software into using the sound of your dog’s barks, the roar of your car’s engine, your favorite guitar lick, or any other crazy sound you could imagine as an IR. Warning: the effects produced can be unpredictable and crazy (but that’s part of the fun!)

Futz

Additionally, you could record an impulse response through any device like your phone, laptop, or car radio speakers and use that to make a target sound seem like it’s playing from that device (a great futz box option, perfect for phone conversations in your next film).

Reverb Tails

Lastly, convolution reverbs are capable of producing an endless amount of long wash reverb tails which make for great scene transitions.

Remember, Convolution Reverb can be a taxing process on your computer’s CPU. If you plan to be using it a lot, try and work with aux/bus tracks to get the most out of your CPU. Video editors using Premiere may want to avoid clip effects and use the track effects for this.

 

Our Favorite Convolution Reverb Plugins

AudioEase Altiverb

Altiverb’s visual displays can really help you find the right room quickly

This is an industry favorite and has proven the test of time. It comes packaged with loads of great IRs from the world over, including domestic rooms and even some cars (this is very useful in post)! The picture and search functions are great too!

Current price: $595

Altiverb XL for surround: $995

 

Waves IR-1

image of Waves IR-L, an included companion to IR-1 that is more friendly on your CPU, but offers fewer controls

A lightweight contender, IR-1 gives you a decent-sized IR library (some very useful stuff in there) and a tweakable toolset to give you what you need for less than half the price of Altiverb.

Current price: $249 (or wait for one of those Waves sales)

IR360 for surround: $299

 

Space Designer

Space Designer’s sleek new interface is much more user-friendly

If you’re an owner and user of Logic Pro, then you can’t beat the free price tag. It once had tons of tweakable features to get lost in but has been updated to be more user-friendly in recent updates. Its IR library will cater more to music than to post-production, but can be used for either.

Current price: free for Logic Pro owners

 

Avid Space

If you are a subscriber to Pro Tools’ subscription, you have access to Space, which is a fantastic reverb tool that comes bundled with a bunch of great IRs as well. Given that Pro Tools is an industry standard post-production tool, its IR library caters to that market more so than Space Designer, whose user base consists more of musicians.

Current price: $499 (or free for Pro Tools subscribers)

 

Of course, these are just a few. There are other great, capable and affordable options out there that are worth checking out and we encourage you to have a look around before you buy.

 

Free Impulses Responses

While most impulse responses you’ll find are provided for free from each plugin’s respective manufacturer, you probably won’t be able to use them as they are likely in their own tool’s proprietary format.

But you’re in luck! To get you started, we’ve identified a few websites that host custom recorded IRs for FREE. No gimmicks either.

OpenAir

This is actually the best source for IRs. Each IR has typically multiple positions (as rooms sound different in different positions). They also give you information about the space, exactly how it was recorded, and what gear was used. They also provide a tool to let you try out the IR on the with your own sound right there on the browser. This website is fantastic!

Fokke van Saane

This gentleman kindly uploaded all of his own personally recorded IRs for anyone to use for free. The site hasn’t been updated for well over a decade but the download links still work. You’ll find more common-place locations like domestic rooms and devices, which will be of great use. Just make sure to download the right format for your plugin. Make sure to shoot him some appreciation as well!

Samplicity

This is a small IR library based around the Bricasti M7 (a famous and expensive hardware reverb unit). Donations can be made if you feel like you got some value out of this. These IRs could help create general reverb rails and washes for all sorts of uses.

 

Wrapping It Up

Convolution reverb may be your new best friend, providing you with ways to mask your ADR, make realistic phone futzes, transition your scenes and get creative.

After you get up and rolling with your convolution plugin, try exploring Soundsnap for cool sound effects to load into your reverb unit and see what kind of effects you could make. Remember, some of the most memorable sounds in film history were made through trial and error.