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Decorrelation

A process in which an audio source signal is transformed into multiple output signals with waveforms that are different from each other but which sound similar. Distributing these signals to different loudspeakers – such as a surround system – creates the sensation of space and helps listeners identify the location of sounds. In nature decorrelation is a product of the delay, reverberation and filtering properties of any room or space. In the studio, effects processors -reverb, delay, chorus, flanger, comb filter, etc. – produce decorrelated output.

There is a long history of home and studio devices that “stereoizemonophonic signals, and they typically worked by decorrelating the output channels. Vocalists have often been recorded twice on separate tracks so that the small variations in the two performances create decorrelation.

The term was originally applied to a technique used in home THX systems to create a more diffuse, full surround sound environment by splitting up the mono surround channel of matrixed surround sound systems (the analog Dolby Surround or Dolby Pro Logic) into two channels and feeding them alternate information. This process, combined with the THX specification of dipole speakers, ensures that the mono surround signal is not localized or located at a specific speaker. Discrete digital surround sound formats (Dolby Digital and DTS) feature stereo, discrete, full-range surround sound channels that don’t require decorrelation.

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