Digital Signal Processing Reference
In-Depth Information
filter useless. In these cases, visual inspection of the obtained response is
mandatory and experimentation with different filter lengths and tolerance
may improve the final result.
l
g
r
,
y
i
d
.
,
©
,
L
s
1
0
0
π/
4
2
π/
4
3
π/
4
π
Figure 7.17
Frequency response of the 17-tap filter meeting the specifications.
Im
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1
Re
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Figure 7.18
Pole-zero plot for the equiripple FIR in Figure 7.17.
7.3 IIR Filter Design
As we mentioned earlier, no optimal procedure exists for the design of IIR
filters. The fundamental reason is that the optimization of the coefficients
of a rational transfer function is a highly nonlinear problem and no satis-
factory algorithm has yet been developed for the task. This, coupled with
the impossibility of obtaining an IIR with linear phase response
(6)
makes
the design of the IIR filter a much less formalized art. Many IIR designed
(6)
It can be proved rigorously that an infinite impulse response with linear phase is neces-
sarily not realizable - think of a sinc filter, for instance.
