DAFX: Digital Audio Effects, Second Edition

4.4 Exciters and Enhancers

4.4.1 Exciters

Introduction

An exciter is a signal processor that emphasizes or de-emphasizes certain frequencies in order to change a signal's timbre. An exciter increases brightness without necessarily adding equalization. The result is a brighter, “airier” sound without the stridency that can sometimes occur by simply boosting the treble. This is often accomplished with subtle amounts of high-frequency distortion, and sometimes by phase shifting. Usually there will only be one or two parameters, such as exciter mix and exciter frequency. The former determines how much “excited” sound gets added to the straight sound, and the latter determines the frequency at which the exciter effect starts [Whi93, And95, Dic87, WG94].

This effect was discovered by the Aphex company and “Aural Exciter” is a trademark of this company. The medium and treble parts of the original signal are processed by a nonlinear circuit that generates higher overtones. These components are then mixed to some extent to the original signal. A compressor at the output of the nonlinear element makes the effect dependent on the input signal. The initial part of percussive sounds will be more enriched than the following part, when the compressor limits the effect depth. The enhanced imaging or spaciousness is probably the result of the phase rotation within the filter [Alt90].

Signal Processing

Measurement results of the APHEX Aural Exciter are shown in Figures 4.39 and 4.40, where the generation ...