1 //
2 // firdes_kaiser_example.c
3 //
4 // This example demonstrates finite impulse response filter design
5 // using a Kaiser window.
6 // SEE ALSO: firdespm_example.c
7 //
8
9 #include <stdlib.h>
10 #include <stdio.h>
11 #include <getopt.h>
12
13 #include "liquid.h"
14
15 #define OUTPUT_FILENAME "firdes_kaiser_example.m"
16
17 // print usage/help message
usage()18 void usage()
19 {
20 printf("firdes_kaiser_example:\n");
21 printf(" u/h : print usage/help\n");
22 printf(" f : filter cutoff frequency, 0 < f < 0.5, default: 0.2\n");
23 printf(" s : filter stop-band attenuation [dB], 0 < s, default: 60\n");
24 printf(" m : fractional sample delay, -0.5 < m < 0.5, default: 0\n");
25 printf(" n : filter length [taps], n > 1, default: 55\n");
26 }
27
main(int argc,char * argv[])28 int main(int argc, char*argv[]) {
29 // options
30 float fc=0.2f; // filter cutoff frequency
31 float As=60.0f; // stop-band attenuation [dB]
32 float mu=0.0f; // fractional timing offset
33 unsigned int h_len=55; // filter length
34
35 int dopt;
36 while ((dopt = getopt(argc,argv,"uhf:n:s:m:")) != EOF) {
37 switch (dopt) {
38 case 'u':
39 case 'h': usage(); return 0;
40 case 'f': fc = atof(optarg); break;
41 case 'n': h_len = atoi(optarg); break;
42 case 's': As = atof(optarg); break;
43 case 'm': mu = atof(optarg); break;
44 default:
45 exit(1);
46 }
47 }
48
49 // validate input
50 if ( fc <= 0.0f ) {
51 fprintf(stderr,"error: %s, filter cutoff frequency must be greater than zero\n", argv[0]);
52 exit(1);
53 } else if ( h_len == 0 ) {
54 fprintf(stderr,"error: %s, filter length must be greater than zero\n", argv[0]);
55 exit(1);
56 }
57
58 printf("filter design parameters\n");
59 printf(" cutoff frequency : %8.4f\n", fc);
60 printf(" stop-band attenuation [dB] : %8.4f\n", As);
61 printf(" fractional sample offset : %8.4f\n", mu);
62 printf(" filter length : %u\n", h_len);
63
64 // generate the filter
65 unsigned int i;
66 float h[h_len];
67 liquid_firdes_kaiser(h_len,fc,As,mu,h);
68
69 // print coefficients
70 for (i=0; i<h_len; i++)
71 printf("h(%4u) = %16.12f;\n", i+1, h[i]);
72
73 // output to file
74 FILE*fid = fopen(OUTPUT_FILENAME,"w");
75 fprintf(fid,"%% %s: auto-generated file\n\n", OUTPUT_FILENAME);
76 fprintf(fid,"clear all;\nclose all;\n\n");
77 fprintf(fid,"h_len=%u;\n",h_len);
78 fprintf(fid,"fc=%12.4e;\n",fc);
79 fprintf(fid,"As=%12.4e;\n",As);
80
81 for (i=0; i<h_len; i++)
82 fprintf(fid,"h(%4u) = %12.4e;\n", i+1, h[i]);
83
84 fprintf(fid,"nfft=1024;\n");
85 fprintf(fid,"H=20*log10(abs(fftshift(fft(h*2*fc,nfft))));\n");
86 fprintf(fid,"f=[0:(nfft-1)]/nfft-0.5;\n");
87 fprintf(fid,"figure; plot(f,H,'Color',[0 0.5 0.25],'LineWidth',2);\n");
88 fprintf(fid,"grid on;\n");
89 fprintf(fid,"xlabel('normalized frequency');\n");
90 fprintf(fid,"ylabel('PSD [dB]');\n");
91 fprintf(fid,"title(['Filter design/Kaiser window f_c: %f, S_L: %f, h: %u']);\n",
92 fc, -As, h_len);
93 fprintf(fid,"axis([-0.5 0.5 -As-40 10]);\n");
94
95 fclose(fid);
96 printf("results written to %s\n", OUTPUT_FILENAME);
97
98 printf("done.\n");
99 return 0;
100 }
101
102