Digital Signal Processing Reference
In-Depth Information
3.4 CONVERSION OF LOW-PASS TO HIGH-PASS FILTERS
In order to maximize the range of filters available in this offering, the normalized
cut-on values for the high-pass filters given in the following chapter have been
chosen to be different to the cut-off values for low pass filters. There is a simple
relationship between the low-pass and high-pass filter, and this has been utilized
to extend the range of filters presented. To convert these low-pass filters into high-
pass filters, the following is carried out:
1. Change the sign of all coefficients.
2. Add 512 to the value of the middle coefficient; that is,
h
L
/2+1
. If the
coefficients are normalized, add 1 to the said coefficient.
3.5 LISTING OF LOW-PASS FILTERS
Table 3.5 gives a list of low-pass filters presented in the following pages. The
filters are listed in increasing order of frequency and filter length.
Table 3.5
Low-Pass Filter Coefficient Listings
Normalized
Frequency
Filter Length,
L
+1
33
55
99
155
255
511
•
0.015
•
0.025
•
0.03
•
0.04
•
0.05
•
•
•
•
•
0.1
•
•
•
•
•
0.15
•
•
•
•
•
•
0.2
•
•
•
•
•
0.25
•
•
•
•
•
•
0.3
•
•
•
•
•
0.35
•
•
•
•
•
•
0.4
•
•
•
•
•
•
0.5
•
•
•
•
•
0.6
•
•
•
•
•
0.7
•
•
•
•
0.8
•
•
•
0.9
