Chapter 4

IIR Digital Filters


4.1      Theory

GIVEN the simplicity and stability of the FIR filter, why would you ever want to consider using an IIR filter? This issue has been debated over the years in numerous articles, papers, and book chapters in the DSP literature. The short answer to the FIR versus IIR question can be distilled down to two brief points.

  1. There is a tremendous amount of analog filter design knowledge available and, as mentioned in Chapter 3, these analog filters are all IIR in nature. There are times when we should take advantage of this wealth of design information.
  2. To meet certain filter design specifications, very high-order FIR filters may be needed. Yet we can usually implement a lower-order (sometimes much lower-order) ...

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