ABSTRACT
There are two commonly used methods for calculating the coefficients of infinite impulse response filters: Direct z-plane design; and Analog filter to digital filter conversion. This chapter uses the following filter naming conventions: LPF: Low-pass filter; HPF: High-pass filter; BPF: Band-pass filter; BSF: Band-stop filter; APF: All-pass filter; HSF: High shelf filter; LSF: Low shelf filter; PEQ: Parametric EQ filter; and GEQ: Graphic EQ system. A more widely used approach to filter design is to first start with the classic analog designs and then convert them into digital versions. Due to the trigonometric identities used in the analog filter conversions, and the fact that the bilinear z transform requires the tan function, the calculations will usually require some kind of trigonometric function. As audio engineers they would also like the parameters to be continuously adjustable so that the user may control them with GUI elements like knobs or sliders.
