Convolution reverb


Convolution reverb

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. 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. The process of convolution multiplies each sample of the audio to be processed (reverberated) with the samples in the impulse response file.

Contents

Creation of impulse responses

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, starter pistol shot or the bursting of a balloon, for instance. A recording of this approximated ideal impulse may be used directly as an impulse response. Techniques involving starter pistols and balloons are sometimes referred to as transient methods, and the response is contained at the beginning of the recording in an impulse.

Another technique, referred to as the sine sweep method, covers the entire audible frequency range, which can result in a broader-range, and higher-quality, impulse response. This involves the use of a longer sound to excite a space (typically a sine sweep), which is then put through a process of deconvolution to produce an impulse response. This approach has the advantage that such sounds are less susceptible to distortion; however, it requires more sophisticated processing to produce a usable impulse response.

A third approach involves using maximum-length sequences, but this is difficult in practice because such sequences are highly susceptible to distortion.

The impulse response of a system is equal to the inverse Fourier Transform of the cross-correlation of the output of the system with the auto-correlation of the input to the system. For example, to sample the acoustic properties of a larger space such as a small church or cathedral, the space can simply be excited using white noise, with the result recorded both near the source, and somewhere else in the space. The coefficients of a finite impulse response can then be generated using the mathematical approach mentioned above.

Applications

Real space simulation

The primary goal of a convolution reverb is to sample real spaces, in order to simulate the acoustics of the sampled space. A straightforward 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 loaded into the convolution processor. This convolution can be applied as part of a signal processing chain.

Machine simulation

It is also possible to sample the impulse response of a reverberation unit, instead of sampling a real space. Thus, it is possible to use a convolution reverb in place of a hardware machine. The techniques used to sample a reverberation unit are the same as the ones used to sample real spaces.

External links


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Reverberation — is the persistence of sound in a particular space after the original sound is removedFact|date=March 2008. When sound is produced in a space, a large number of echoes build up and then slowly decay as the sound is absorbed by the walls and air,… …   Wikipedia

  • Allen Organ — Company, formed in 1939 by Jerome Markowitz, is located in Macungie, Pennsylvania. It is one of the world s largest builders of electronic organs. Allen introduced the world s first digital musical instrument in 1971(… …   Wikipedia

  • Impulse response — The Impulse response from a simple audio system. Showing the original impulse, the response after high frequency boosting, and the response after low frequency boosting. In signal processing, the impulse response, or impulse response function… …   Wikipedia

  • Convolute — may also refer to: Convolution (mathematics and music) Circular convolution Convolution reverb Convolution sampling Convolution theorem Titchmarsh convolution theorem Dirichlet convolution Infimal convolute Logarithmic convolution Vandermonde… …   Wikipedia

  • Logic Express — Infobox Software name = Logic Express caption = developer = Apple Computer latest release version = 8.0.2 latest release date = 2008 05 29 operating system = Mac OS X genre = MIDI Sequencer + Digital Audio Workstation license = Proprietary… …   Wikipedia

  • Logic Studio — Infobox Software name = Logic Studio caption = developer = Apple Inc. latest release version = 1.0 latest release date = 2007 09 12 operating system = Mac OS X genre = Music production license = Proprietary website =… …   Wikipedia

  • Drumagog — is an audio plug in that performs real time drum replacement[1], developed by WaveMachine Labs in 1999[2]. The latest version of the software is Drumagog 5, released in October, 2010. Contents 1 Drumagog 5 2 Release His …   Wikipedia

  • Faltungshall — Der Faltungshall ist ein akustischer Hall Effekt, der mit Hilfe der Faltung Abbilder real existierender Räume per Computersystem auf Audiosignale errechnet. Inhaltsverzeichnis 1 Allgemeines 2 Besonderheiten 3 Grundprinzip …   Deutsch Wikipedia

  • Finite impulse response — A finite impulse response (FIR) filter is a type of a digital filter. The impulse response, the filter s response to a Kronecker delta input, is finite because it settles to zero in a finite number of sample intervals. This is in contrast to… …   Wikipedia

  • Kontakt — is a software sampler made by Native Instruments. It runs on Macintosh and Microsoft Windows platforms, available in standalone and plug in formats (VST, AU, DXi, RTAS). Concept Kontakt was envisioned as a new breed software sampler, the original …   Wikipedia