An [[Elliptic Function|Elliptic]] [[Signal Filter|Filter]] is a mix of a [[Infinite Impulse Response Filters|Feedback Filter]] and a [[Finite Impulse Response Filters|Feed Forward Filter]]. $\huge \begin{align} \mathcal{H} (z) &= \frac{1+az^{-1}+bz^{-2}}{1+c z^{-1}+dz^{-2}} \end{align} $ $\huge a,b,c,d \in \R $ $ \omega $