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Separating the Transfer Function Numerator and Denominator

From Eq.$ \,$(6.5) we have that the transfer function of a recursive filter is a ratio of polynomials in $ z$:

$\displaystyle H(z) = \frac{B(z)}{A(z)} \protect$ (8.4)

where

\begin{eqnarray*} B(z) &=& b_0 + b_1 z^{-1}+ \cdots + b_M z^{-M}\\ A(z) &=& 1 + a_1 z^{-1}+ \cdots + a_N z^{-N}. \end{eqnarray*}

By elementary properties of complex numbers, we have

\begin{eqnarray*} G(\omega) &=& \frac{\left\vert B(e^{j\omega T})\right\vert}{\... ...a(\omega) &=& \angle B(e^{j\omega T}) - \angle A(e^{j\omega T}). \end{eqnarray*}

These relations can be used to simplify calculations by hand, allowing the numerator and denominator of the transfer function to be handled separately.

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