1 //
2 // firhilb_example.c
3 //
4 // Hilbert transform example. This example demonstrates the
5 // functionality of firhilbf (finite impulse response Hilbert transform)
6 // which converts a complex time series into a real one and then back.
7 //
8 // SEE ALSO: firhilb_interp_example.c
9 // firhilb_example.c
10 //
11
12 #include <stdio.h>
13 #include <complex.h>
14 #include <math.h>
15
16 #include "liquid.h"
17
18 #define OUTPUT_FILENAME "firhilb_example.m"
19
main()20 int main() {
21 unsigned int m = 7; // Hilbert filter semi-length
22 float As = 60.0f; // stop-band attenuation [dB]
23 float fc = 0.123456; // signal center frequency
24 unsigned int num_input_samples=128; // number of samples
25
26 // derived values
27 unsigned int h_len = 4*m+1; // filter length
28 unsigned int num_total_samples = num_input_samples + h_len;
29
30 // create Hilbert transform object
31 firhilbf qi = firhilbf_create(m,As); // interpolator
32 firhilbf qd = firhilbf_create(m,As); // decimator
33 firhilbf_print(qi);
34
35 // data arrays
36 float complex x[ num_total_samples]; // complex input
37 float y[2*num_total_samples]; // real output
38 float complex z[ num_total_samples]; // complex output
39
40 // initialize input array
41 unsigned int i;
42 for (i=0; i<num_total_samples; i++) {
43 x[i] = cexpf(_Complex_I*2*M_PI*fc*i) +
44 cexpf(_Complex_I*2*M_PI*fc*i*1.3f)*0.1f;
45 x[i] *= (i < num_input_samples) ? 1.855f*hamming(i,num_input_samples) : 0.0f;
46 }
47
48 // execute interpolator (complex to real conversion)
49 firhilbf_interp_execute_block(qi, x, num_total_samples, y);
50
51 // execute decimator (real to complex conversion)
52 firhilbf_decim_execute_block(qd, y, num_total_samples, z);
53
54 // destroy Hilbert transform object
55 firhilbf_destroy(qi);
56 firhilbf_destroy(qd);
57
58 //
59 // export results to file
60 //
61 FILE*fid = fopen(OUTPUT_FILENAME,"w");
62 fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
63 fprintf(fid,"clear all;\n");
64 fprintf(fid,"close all;\n");
65 fprintf(fid,"h_len=%u;\n", 4*m+1);
66 fprintf(fid,"num_input_samples=%u;\n", num_input_samples);
67 fprintf(fid,"num_total_samples=%u;\n", num_total_samples);
68 fprintf(fid,"tx = 0:(num_total_samples-1);\n");
69 fprintf(fid,"ty = [0:(2*num_total_samples-1)]/2;\n");
70 fprintf(fid,"tz = tx;\n");
71
72 for (i=0; i<num_total_samples; i++) {
73 // print results
74 fprintf(fid,"x(%3u) = %12.4e + %12.4ej;\n", i+1, crealf(x[i]), cimagf(x[i]));
75 fprintf(fid,"y(%3u) = %12.4e;\n", 2*i+1, y[2*i+0]);
76 fprintf(fid,"y(%3u) = %12.4e;\n", 2*i+2, y[2*i+1]);
77 fprintf(fid,"z(%3u) = %12.4e + %12.4ej;\n", i+1, crealf(z[i]), cimagf(z[i]));
78 }
79
80 fprintf(fid,"figure;\n");
81 fprintf(fid,"subplot(3,1,1);\n");
82 fprintf(fid," plot(tx,real(x),'Color',[0.00 0.25 0.50],'LineWidth',1.3,...\n");
83 fprintf(fid," tx,imag(x),'Color',[0.00 0.50 0.25],'LineWidth',1.3);\n");
84 fprintf(fid," legend('real','imag','location','northeast');\n");
85 fprintf(fid," ylabel('transformed/complex');\n");
86 fprintf(fid," axis([0 num_total_samples -2 2]);\n");
87 fprintf(fid," grid on;\n");
88 fprintf(fid,"subplot(3,1,2);\n");
89 fprintf(fid," plot(ty,y,'Color',[0.00 0.25 0.50],'LineWidth',1.3);\n");
90 fprintf(fid," ylabel('original/real');\n");
91 fprintf(fid," axis([0 num_total_samples -2 2]);\n");
92 fprintf(fid," grid on;\n");
93 fprintf(fid,"subplot(3,1,3);\n");
94 fprintf(fid," plot(tz,real(z),'Color',[0.00 0.25 0.50],'LineWidth',1.3,...\n");
95 fprintf(fid," tz,imag(z),'Color',[0.00 0.50 0.25],'LineWidth',1.3);\n");
96 fprintf(fid," legend('real','imag','location','northeast');\n");
97 fprintf(fid," ylabel('transformed/complex');\n");
98 fprintf(fid," axis([0 num_total_samples -2 2]);\n");
99 fprintf(fid," grid on;\n");
100
101 // plot results
102 fprintf(fid,"nfft=4096;\n");
103 fprintf(fid,"%% compute normalized windowing functions\n");
104 fprintf(fid,"X=20*log10(abs(fftshift(fft(x/num_input_samples,nfft))));\n");
105 fprintf(fid,"Y=20*log10(abs(fftshift(fft(y/num_input_samples,nfft))));\n");
106 fprintf(fid,"Z=20*log10(abs(fftshift(fft(z/num_input_samples,nfft))));\n");
107 fprintf(fid,"f =[0:(nfft-1)]/nfft-0.5;\n");
108 fprintf(fid,"figure; plot(f+0.5,X,'LineWidth',1,'Color',[0.50 0.50 0.50],...\n");
109 fprintf(fid," f*2, Y,'LineWidth',2,'Color',[0.00 0.50 0.25],...\n");
110 fprintf(fid," f+0.5,Z,'LineWidth',1,'Color',[0.00 0.25 0.50]);\n");
111 fprintf(fid,"grid on;\n");
112 fprintf(fid,"axis([-1.0 1.0 -80 20]);\n");
113 fprintf(fid,"xlabel('normalized frequency');\n");
114 fprintf(fid,"ylabel('PSD [dB]');\n");
115 fprintf(fid,"legend('original/cplx','transformed/real','regenerated/cplx','location','northeast');");
116
117 fclose(fid);
118 printf("results written to %s\n", OUTPUT_FILENAME);
119
120 printf("done.\n");
121 return 0;
122 }
123