Imagine that in your project within a DAW, an awesome synth lead or guitar solo sounds as if it’s being played inside a real-life Viennese theater—with impeccable acoustics and rich room ambience. That’s essentially what convolution reverb does on your music-making computer.
It is widely believed that the inventor of this spatial processing method was German scientist and engineer Manfred R. Schroeder. In the 1950s, he theoretically described the possibility of electronically reproducing the acoustics of actual rooms and even partially open spaces. He discovered that by playing back a very short broadband sound impulse in a given space and recording the reflected sound, this recording could later be used to realistically simulate the reverberation of the room electronically.
However, for many years implementing the technology was nearly impossible because hypothetical electronic devices capable of doing so would have had to perform complex calculations in real time. It wasn't until 1999 when Sony introduced the world's first convolution reverb processor, the DRE-S777, which handled these operations “on-the-fly.”
If we don't delve too deeply into technicalities, here's how it works: specialists arrive at the chosen location and wait for silence—for example, during night hours when there are few sources of unwanted noise. Using specialized equipment, they produce a loud broadband "click" in the room. The echoes of the room are then recorded using high-quality microphones. This recording is commonly referred to as an "impulse response." Typically, such recordings are captured through professional audio interfaces into high-resolution WAV files. Sometimes portable recorders with excellent quality are also employed.
These recorded room responses are subsequently loaded into physical hardware units or virtual reverb plugins. To put it simply, algorithms in these devices combine the "dry" signal from any source—such as vocals, acoustic instrument recordings, synthesizer tones, or drum hits—and overlay them with the tail of sound reflections captured in a real environment.
Despite its relative youth, convolution technology has already reached remarkable heights. Over time, it's become clear that one can create not only sonic imprints of physical spaces but also replicate the behavior of various pieces of musical gear. It's exactly this principle behind digital devices and software that model, say, the sound of guitar and bass amps, individual amplifiers, and speaker cabinets.
There are solutions simulating the unique characteristics of spring and plate reverbs. And despite the somewhat paradoxical nature of what's happening—even other popular digital processors themselves can now be modeled via convolution techniques.
Initially, comfortable use of software versions of convolution reverbs required relatively powerful computers. But over time, both the plugins became more optimized, and affordable PCs significantly increased their performance capabilities. Nowadays, a convolution reverb can be a daily tool even for beginner bedroom producers and lone sound designers.
What attracts most people to this technology is its realism. This feature is particularly appealing to many professionals. In the music industry, composers working on film scores, video games, trailers, and high-end advertisements find it invaluable. After all, placing a sampled virtual orchestra in, say, Sydney Opera House can sometimes be priceless.
In the realm of listening music—that is, artistic music—convolution reverb is utilized by producers who prioritize realistic-sounding vocals and instruments. Additionally, simulating physical spaces during spatial processing can address numerous creative challenges. For instance, creating a recording for a neo-punk band that sounds as though it were made in a rehearsal room. Or aging certain instruments' timbre in an arrangement, setting up a dialogue between different eras. Or achieving moments where the vocalist's voice sounds almost angelic due to blending with genuine reflections from an existing ancient cathedral known for its distinctive acoustics.
Convolution reverb is frequently applied in Foley work, game audio production, advertising, and trailer creation. As practical experience shows, even an unsophisticated general audience appreciates the realism of sound design when echoes from authentic locations relevant to the depicted events are incorporated.
Today, much content is filmed in studios or created using CGI, yet there's still a desire to add realistic sound. Therefore, departments responsible for sound in film crews or gaming companies often seek out locations featuring objects similar to those described in scripts: stadiums, hangars, caves, ravines, man-made underground chambers, etc., and record custom impulse responses there. These recordings are then used to enhance the visual elements with lifelike audio.
On low-budget productions, sound engineers across various types of content rely on pre-recorded Impulse Responses (IRs) of existing physical spaces available commercially and often quite affordably. There are also fully free convolution reverb plugins and collections of free impulse responses, although they're less common.
There's no genre where convolution reverb feels inappropriate. Even some producers of electronic music occasionally want to soften the overly sterile and harsh sound of synthetic instruments and samples. Indeed, placing elements of such tracks into realistic spaces can give them added depth and an extra auditory dimension.
Certainly, algorithmic reverbs do exist, offering settings for size, basic shape, and type of room—down to wall material. However, their modeling capabilities remain limited. Acoustically interesting real-world spaces are architecturally complex entities, making it non-trivial and resource-intensive to mathematically model their intricate forms. The same applies to many urban, industrial, and especially natural locations.
It's far cheaper, faster, and computationally efficient to utilize impulse responses of real spaces. Moreover, real locations resonate with such variety—offering wide and complex stereo responses (if recorded in stereo), multiple sound repetitions, and distant rolling echoes—that imagining such effects while sitting in a studio is challenging.
A great way to start exploring convolution reverb is with the well-optimized MConvolutionEZ plugin included in the completely free MFreeFXBundle package from Czech company Melda Production. This plugin comes equipped with libraries of impulses from rooms, halls, churches, and allows you to experiment with cabinet simulation, plate reverbs, and more.
Perhaps convolution reverbs are just the spice missing from your musical production. If you've never tried them before, give them a shot—the results might surprise you!
Yes, fortunately, some developers of free plugins also provide impulse responses. You can also load third-party libraries, whether commercial or noncommercial, right into the aforementioned MConvolutionEZ.
Here's the catch: finding high-quality free IRs will require spending considerable time searching. We'll save you some effort here. On GitHub, you'll find a list of links to several intriguing libraries.
For instance, among these resources, you'll discover Echothief, a free collection containing over 100 US-based real-world spaces. Among these are unusual places like a riverbed beneath Byron Glacier or the sacred "cathedral-like" chamber of Shasta Lake Cave. You'll also find IRs of human-built structures, such as Cedarburg's covered bridge in Wisconsin.
Also in this list, you'll find download links for IRs provided by the Centre for Digital Music at Queen Mary, University of London. This collection includes responses from fascinating large halls, such as an octagonal Victorian building constructed in 1888 originally designed as a library.
Upon closer inspection, you may even uncover free impulses from a Masonic hall in Winnipeg boasting acoustics described by its creators as "stunning."
Of course, commercial libraries of convolution reverb impulses offer greater diversity, potentially encompassing hundreds upon hundreds of venues. For instance, Impulse Record freely distributes the high-quality Convology XT plugin, but purchasing additional IRs for it remains necessary...
Convolution reverb with IRs of real-world spaces enables us to achieve something unimaginable just decades ago: seamlessly blending unrealistic synthetic and hybrid sounds with the authentic resonance of our planetary environment. When skillfully applied, this technique opens up boundless possibilities for enhancing creativity and immersion in sound design.
By the way, you're probably starting to realize what kind of small business opportunity exists once armed with reasonably priced equipment for capturing impulse responses of buildings and natural landscapes. Just remember, as they say, during the Klondike Gold Rush, the ones who profited most weren't the miners but those selling shovels to them.
