Finite Impulse Response Filters - Digital Signal Processing and Applications with the C6713 and C6416 DSK - page 149

// bp55.cof Coefficients for FIR bandpass filter centered @ Fs/4

#define N 55 //number of coefficients

float h[N]=
{1.7619E-017, 7.0567E-003, 2.2150E-018,-1.0962E-002, 4.0310E-017,
1.3946E-002, 7.1787E-018,-1.4588E-002, 3.9928E-017, 1.1474E-002,
5.9881E-018,-3.5159E-003,-6.6174E-018,-9.7476E-003,-1.7919E-017,
2.7932E-002,-9.4329E-017,-4.9740E-002, 3.3834E-017, 7.3066E-002,
-3.6228E-017,-9.5284E-002, 3.2194E-017, 1.1365E-001,-2.2165E-017,
-1.2576E-001, 7.8980E-018, 1.3000E-001, 7.8980E-018,-1.2576E-001,
-2.2165E-017, 1.1365E-001, 3.2194E-017,-9.5284E-002,-3.6228E-017,
7.3066E-002, 3.3834E-017,-4.9740E-002,-9.4329E-017, 2.7932E-002,
-1.7919E-017,-9.7476E-003,-6.6174E-018,-3.5159E-003, 5.9881E-018,
1.1474E-002, 3.9928E-017,-1.4588E-002, 7.1787E-018, 1.3946E-002,
4.0310E-017,-1.0962E-002, 2.2150E-018, 7.0567E-003, 1.7619E-017};
FIGURE 4.18. Coefficient file in float format for a FIR bandpass filter centered at F s /4
( BP55.cof ).

55-coefficient FIR bandpass filter with a center frequency at F s /4. A filter develop-
ment package (on the CD) that generates filter coefficients in float or hexadecimal
format is described in Appendix E.
Build this project as FIRPRN . Run this project (with the coefficient file BP55.cof )
and verify that the output is an FIR bandpass filter centered at 2 kHz. To verify the
output as the noise sequence, output dly[0] in lieu of yn when calling the func-
tion output_sample.

Testing Different FIR Filters
Halt the program. Edit the C source program to include and test different coeffi-
cient files (on the CD) that represent different FIR filters, all using float format
values. Each coefficient file contains 55 coefficients (except comb14.cof ).

1. BP55.cof : bandpass with center frequency F s /4
2. BS55.cof : bandstop with center frequency F s /4
3. LP55.cof : lowpass with cutoff frequency F s /4
4. HP55.cof : highpass with bandwidth F s /4
5. Pass2b.cof : with two passbands
6. Pass3b.cof : with three passbands
7. Pass4b.cof : with four passbands
8. Comb14.cof : with multiple notches (comb filter)

These filters were designed with MATLAB (see Appendix D). Figure 4.19 a shows
the real-time output frequency response of an FIR filter with two passbands, using