Digital Signal Processing Reference
In-Depth Information
The bandwidth
F
-3dB
, at the -3 dB level (i.e. amplitude of 0.71) depends on the
filter order
L
. An increase in filter order means an increase in
F
-3dB
; however the
rate of increase with respect to filter order decreases progressively leading to
saturation for large
L
. This aspect is best captured by plotting 1/(
W
-
F
-3dB
)
against filter length
L
+1, which is linear with a slope of 0.396 (see Figure 5.1(b)).
5.1.5
Conversion to Band-Stop Filters
Every band-pass filter presented here can be converted into a band-stop (reject)
filter with the pass-band becoming the stop-band. The following formula is used
to convert band-pass into band-stop filters
L
h
k
+
1
BP
,
k
2
h
=
(5.3)
BS
,
k
512
h
k
=
L
+
1
L
BP
,
+
1
2
2
where
h
BP
and
h
BS
are the band-pass and band-stop filter coefficients respectively.
5.1.6
Overview of Band-Pass Filter Coefficients
Table 5.1 gives a listing of the band-pass filters available in this offering. They
have been divided into groups with bandwidths of 0.05, 0.1, 0.2, and 0.3. The
filters are presented in increasing order of filter length but decreasing order of
filter bandwidth in a similar manner to Table 5.1.
