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In audio signal processing, convolution reverb is a process for digitally simulating the reverberation of a physical or virtual space. It is based on the mathematical convolution operation, and uses a pre-recorded audio sample of the impulse response of the space being modelled.

An impulse response is a recording of the reverberation that is caused by an acoustic space when an ideal impulse is played. However, an ideal impulse is a mathematical construct, and cannot exist in reality, as it would have to be infinitesimally narrow in time. Therefore, approximations have to be used; the sound of an electric spark or a gun shot, for instance. Alternatively, a more complex approach may be taken, such as using maximum-length sequences.

To apply the reverberation effect, the impulse-response recording is first stored in a digital signal-processing system. This is then convolved with the incoming audio signal to be processed.

Contents 1 Applications 1.1 Real space simulation 1.2 Machine simulation 1.3 Synthesized impulse responses 2 External links

The primary goal of a convolution reverb is to sample real spaces, in order to simulate the acoustics of the sampled space.

A straight forward and simple mono example of capturing an impulse response would be to set up a microphone in a concert hall and to place the microphone in the centre of the auditorium.

Next, produce a very brief pulse (often an electric spark) of sound, and record everything that the microphone picks up, which includes both the original sound and the response of the room to it.

The recorded take would then be cleanly edited and then loaded into the convolution processor. This convolution can be applied as part of a signal processing chain.

It is also possible, instead of sampling a real space, to sample a reverberation unit. Thus, it is supposedly possible to use a convolution reverb in place, for instance, of a hardware machine.

The techniques used to sample a reverberation unit are the same as the ones used to sample real spaces.

Impulse responses can also be synthesized. Impulse response synthesis can be based on a lot of different techniques :

• acoustic modelization, like in Voxengo's Impulse Modeler software
• "shaping" of white or pink noise, which would be a method similar to subtractive synthesis
• use of oscillator spectra

...anything is possible.

Depending on the degree of realism, the convolution reverb will act not only as a space processor, but also as a special effect processor.

• - Examples of sampled impulse responses to be used in convolution reverbs (Fokke Van Saane)
• - Examples of impulse responses synthesized from oscillator spectra, to be used in convolution reverbs (Emmanuel Deruty)