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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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