As the zero is moved farther away from the circle, the notch becomes less deep until finally the zero is farther from the circle than the pole and the notch has become a hump. The resulting filter which will be called pole on pedestal is in many respects like the narrowband filter discussed earlier. Some of these filters are illustrated in Figures 18 and 19 . The former is flat, while the latter continues to decay with increasing . 2-18 Figure 18 Pole and zero locations for some simple filters.
Circles are unit circles in the Z plane.
Each has one pole at . A second pole at enables the filters to be real in the time domain. Narrowband filters and sharp cutoff filters should be used with caution. An ever-present penalty for such filters is that they do not decay rapidly in time. Although this may not present problems in some applications, it will do so in others.