Summary of Flanging

In view of the above, we may define a flanger in general as any filter which modulates the frequencies of a set of uniformly spaced notches and/or peaks in the frequency response. The main parameters are

• Depth -- controlling notch depth
• Speed -- speed of notch movement
• Phase -- switch to subtract instead of adding the direct signal with the delayed signal

Possible additional parameters include

• Average Delay
• Excursion or Sweep -- amount by which the delay-line grows or shrinks
• Feedback or Regeneration -- feedback coefficient from output to input

Note that flanging provides only uniformly spaced notches. This can be considered non-ideal for several reasons. First, the ear processes sound over a frequency scale that is more nearly logarithmic than linear [459]. Therefore, exponentially spaced notches (uniformly spaced on a log frequency scale) should sound more uniform perceptually. Secondly, the uniform peaks and notches of the flanger can impose a discernible ``resonant pitch'' on the program material, giving the impression of being inside a resonant tube. Third, when (inverted flanging), it is possible for a periodic tone to be completely annihilated by harmonically spaced notches if the harmonics of the tone are unlucky enough to land exactly on a subset of the harmonic notches. In practice, exact alignment is unlikely; however, the signal loudness can be modulated to a possibly undesirable degree as the notches move through alignment with the signal spectrum. For this reason, flangers are best used with noise-like or inharmonic sounds. For harmonic signals, it makes sense to consider methods for creating non-uniform moving notches.

A Faust software implementation of flanging may be found in the file effect.lib within the Faust distribution [154,170]. The Faust programming example phaser_flanger.dsp may be run to hear the effect on a test signal and experiment with its parameters in real time.

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About the Author: Julius Orion Smith III
Julius Smith's background is in electrical engineering (BS Rice 1975, PhD Stanford 1983). He is presently Professor of Music and Associate Professor (by courtesy) of Electrical Engineering at Stanford's Center for Computer Research in Music and Acoustics (CCRMA), teaching courses and pursuing research related to signal processing applied to music and audio systems. See http://ccrma.stanford.edu/~jos/ for details.

I am currently implementing a flanger filter and would like to try to add non-uniform moving notches. Do you have a reference for that type of effect?

Sorry, I just read on the next page about phasers and that seems to be what I am looking for :) I was simply to keyboard trigger happy today...