Modeling the Harmonic Exciter

Dec 2012

  • This research will be presented at the 135th International Convention of the Audio Engineering Society (AES) in NYC on 17th Oct 2013.

Effect Samples




  • To recreate the “vintage” style effect of the APHEX Aural Exciter, an audio effects processor used to enhance the brightness and clarity of a sound, particularly vocals. This original analog hardware unit is to be digitally modeled, and implemented as a standalone application.


  • The exciter’s timbre is described as having a bright, airy or sparkly feel, free of the harshness that can sometimes result from equalizer treble boost. It introduces a measured amount of high-frequency distortion to achieve this.
  • The original 1979 patent for the APHEX Aural Exciter was closely referenced for technical specifications.
  • The exciter’s 2nd-order Butterworth highpass characteristic and cubic non-linearity were first modeled in MATLAB, and then transferred to FAUST code.
  • The digital model was generated as a standalone application in Qt by the FAUST compiler.
  • Apple Logic Pro’s digital exciter effect provided a “ballpark” check on filter response – frequency response and input vocal plosive (percussive) consonants were inspected.
  • The digital model’s performance is closely matched with the Logic Pro exciter.

Future Work

  • It is pertinent to take recordings of the original APHEX Aural Exciter to imitate its characteristic more closely (unable to be sourced for this study).
  • It may be desirable to have a user-selectable even/odd harmonics ratio, as in the present-day APHEX offering. This can be achieved by designing a smooth transition between asymmetric clipping, which generates more even harmonics, and symmetric clipping, which generates more odd harmonics.

Presentation Deck

Final Report

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