Convolution Reverb

Convolution reverb is a process that mimics the reverberation of a physical or a virtual space. When used in audio signal processing, it occupies several software profiles that are capable of recreating a particular audio environment. Convolution reverb can recreate a realistic simulation of any acoustic space.

The Workings of the Convolution Reverb

Convolution reverb has a fairly simple operation. First, someone plays an audio sample, a snare hit, or a sine sweep tone in a real space and a microphone captures its impulse response. After that, the audio sample is fed into the convolution processor. Finally, the incoming signal replicates the unique sound of that space. In summary, a sound enters an acoustic space. As a result, the impulse response of that space is recorded to react to a completely different signal. 

This software plugin processes early reflections and diffused reflections. On the one hand, it captures early reflections as a result of sounds striking through various surfaces. These reflections are discrete and appear as peaks. On the other, it captures diffused reflections due to the presence of many surfaces and objects. The result: the audience perceives these reflections as continuous noise.

Impulse Response

The most frequently used convolution reverbs are TL Space Native Edition-Trillium Lane Labs, Space Designer-Logic Pro, IR 1-Wave, and Altiverb-Audio Ease.

An impulse response (IR) is an audio sample recorded by the excitation of an acoustic space. An impulse response involves the complete information regarding the reverb of the space, including reverberant decay characteristics, arrival times, frequency of sounds, discrete reflections, signal-to-noise ratio, and an ability to reproduce human speech. When focusing on acoustical analysis, some can recognize the impulse as an acoustical signature of a system.

Convolution Reverb: the Sine Sweep and the Short Impulse Methods

The sine sweep method and the short impulse method are the most common techniques to recreate impulse responses. The sine sweep method involves a long sine wave tone that produces reverberation for all the frequencies. Therefore, it creates a high-quality simulation of a specific space. The short impulse method involves the creation and recording of very short impulses, such as balloon bursts and clapping. Sound engineers find it more rewarding to create sounds that are pleasant to the human ear than to create technically perfect sounds. Hence, experimentation is an essential part of the musical universe. 

A Final Little Bit of History

Around 1976, people used digital reverb based on multiple feedback delay lines, which offered tones that didnt’t sound realistic. In 1999, more or less, Sony developed the first real-time convolution processor: he DRE S777. This device processed impulse responses rather quickly, so it revolutionized the audio universe. Nowadays, the most popular convolution processor is the DSP.