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Physical Audio Signal Processing
    Time-Varying Delay Effects
       Specific Time-Varying Delay Effects
          Flanging
             Flanger Inverted Mode

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Flanger Inverted Mode

A different type of maximum depth is obtained for $ g=-1$. In this case, the peaks and notches of the $ g=1$ case trade places. In practice, the depth control $ g$ is usually constrained to the interval $ [0,1]$, and a sign inversion for $ g$ is controlled separately using a ``phase inversion'' switch.

In inverted mode, unless the delay $ M$ is very large, the bass response will be weak, since the first notch is at dc. This case usually sounds high-pass filtered relative to the ``in-phase'' case ($ g>0$).

As the notch spacing grows very large ($ M$ shrinks), the amplitude response approaches that of a first-order difference $ y(n) = x(n) - x(n-1)$, which approximates a differentiator $ y(t) = \frac{d}{dt}x(t)$. An ideal differentiator eliminates dc and provides a progressive high-frequency boost rising 6 dB per octave (specifically, the amplitude response is $ \left\vert H(\omega)\right\vert = \left\vert\omega\right\vert$).

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Next: Flanger Feedback Control
written by 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.