next up previous contents index
Next: Real outputs from complex Up: Designing filters Previous: Elementary recirculating filter   Contents   Index

Compound filters

We can use the recirculating and non-recirculating filters developed here to create a compound filterby putting several elementary ones in series. If the parameters of the non-recirculating ones (of the first type) are ${Q_1}, \ldots, {Q_j}$ and those of the recirculating ones are ${P_1}, \ldots, {P_k}$, then putting them all in series, in any order, will give the transfer function:

\begin{displaymath}
H(Z) = {
{
(1 - {Q_1}{Z^{-1}}) \cdots (1 - {Q_j}{Z^{-1}})
} \over {
(1 - {P_1}{Z^{-1}}) \cdots (1 - {P_k}{Z^{-1}})
}
}
\end{displaymath}

The frequency response of the resulting compound filter is the product of those of the elementary ones. (One could also combine elementary filters by adding their outputs, or making more complicated networks of them; but for most purposes the series configuration is the easiest one to deal with.)



Miller Puckette 2005-02-21