Databases Reference
In-Depth Information
Low-pass
filter
Low-pass
filter
High-pass
filter
Low-pass
filter
Low-pass
filter
High-pass
filter
High-pass
filter
Low-pass
filter
Low-pass
filter
High-pass
filter
High-pass
filter
High-pass
filter
Low-pass
filter
High-pass
filter
F I GU R E 14 . 5
An eight-band filter bank.
T A B L E 14 . 1
Coefficients for the eight-tap
Johnston low-pass filter.
h
0
,
h
7
0
.
00938715
h
1
,
h
6
0
.
06942827
h
2
,
h
5
−
0
.
07065183
h
3
,
h
4
0
.
48998080
Another popular set of filters are the Smith-Barnwell filters [
205
], some of which are shown
in Tables
14.4
and
14.5
.
These families of filters differ in a number of ways. For example, consider the Johnston
eight-tap filter and the Smith-Barnwell eight-tap filter. The magnitude transfer functions for
these two filters are plotted in Figure
14.6
. Notice that the cutoff for the Smith-Barnwell filter
is much sharper than the cutoff for the Johnston filter. This means that the separation provided
by the eight-tap Johnston filter is not as good as that provided by the eight-tap Smith-Barnwell
filter. We will see the effect of this when we look at image compression later in this chapter.
These filters are examples of some of the more popular filters. Many more filters exist in
the literature, and more are being discovered.
