P. Dutilleux and U. Zölzer
Audio effect algorithms for dynamics processing, valve simulation, overdrive and distortion for guitar and recording applications, psychoacoustic enhancers and exciters fall into the category of nonlinear processing. They create intentional or unintentional harmonic or inharmonic frequency components which are not present in the input signal. Harmonic distortion is caused by nonlinearities within the effect device. We will discuss nonlinear processing in three main musical categories. The first category consists of dynamic range controllers where the main purpose is the control of the signal envelope according to some control parameters. The second class of nonlinear processing is designed for the creation of strong harmonic distortion such as guitar amplifiers and guitar effect processors. The third category is represented by signal processing devices called exciters and enhancers. Their main field of application is the creation of additional harmonics for a subtle improvement of the main sound characteristic.
Keywords: Nonlinear Systems, Dynamics Processing, Nonlinear Distortion, Limiting, Compression, Expansion, Harmonic Distortion, Exciters