### Spectral Roll-Off

**Definition: **A function
is said to be of order
if
there exist
and some positive constant
such
that
for all
.

**Theorem: **(*Riemann Lemma*):
If the derivatives up to order
of a function
exist and are
of bounded variation, then its Fourier Transform
is
asymptotically of order
, *i.e.*,

(3.42) |

*Proof: *See §B.18.

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