IIR Filter

IIR (Infinite Impulse Response) Filters are implemented as zero-phase Chebyshev filter designed as a cascade of a 4 poles Low-Pass Filter, a 4-poles High Pass Filter and a 2 poles notch filter. Zero-Phase is obtained using the forward-backward filtering technique: signals are filtered twice, one in the forward direction, and the other one after reversing the signal. Ripple is set to 0.5%.

"Chebyshev filters are used to separate one band of frequencies from another. Although they cannot match the performance of the windowed-sinc filter, they are more than adequate for many applications. The primary attribute of Chebyshev filters is their speed, typically more than an order of magnitude faster than the windowed-sinc. This is because they are carried out by recursion rather than convolution."

From "The Scientist and Engineer's Guide to Digital Signal Processing", By Steven W. Smith, Ph.D.

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