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Spectral Roll-Off



Definition: A function $ W(\omega)$ is said to be of order $ 1/\omega^{n+1}$ if there exists $ \omega_0$ and some positive constant $ M<\infty$ such that $ \left\vert W(\omega)\right\vert<M/w^{n+1}$ for all $ \omega > \omega_0$.



Theorem: (Riemann Lemma): If the derivatives up to order $ n$ of a function $ w(t)$ exist and are of bounded variation, then its Fourier Transform $ W(\omega)$ is asymptotically of order $ 1/\omega^{n+1}$, i.e.,

$\displaystyle W(\omega) = {\cal O}\left(\frac{1}{\omega^{n+1}}\right),
\quad(\hbox{as }\omega\to\infty)
$

Proof: See §B.2.


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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.


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