Digital Filter Design
In this chapter we outline some of the best-known methods for designing non-recursive and recursive digital filters. Although almost any DSP algorithm or processor can reasonably be described as a ‘filter’, the term is commonly reserved for processors which transmit (or reject) well-defined frequency ranges. Typical, idealised, magnitude characteristics of four digital filter categories are shown in figure 2.1. Remember that although the frequency response of a digital processor is always repetitive in form, its performance over the range 0 ≤ Ω ≤ π defines the filtering action on any adequately-sampled signal. For example, a filter having a response peak at Ω = π (and therefore also at Ω = 3π, 5π, ... ) is described as ‘high pass’.
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