\begin{definition}[Definition:Filtering Function]
The '''filtering function''' is the real function $\operatorname {sinc}: \R \to \R$ defined as:
:$\forall x \in \R: \map {\operatorname {sinc} } x := \dfrac {\sin \pi x} {\pi x}$
where $\sin$ denotes the (real) sine function.
\end{definition}