1 //
2 // iirfilt_crcf_example.c
3 //
4 // Complex infinite impulse response filter example. Demonstrates
5 // the functionality of iirfilt by designing a low-order
6 // prototype (e.g. Butterworth) and using it to filter a noisy
7 // signal. The filter coefficients are real, but the input and
8 // output arrays are complex. The filter order and cutoff
9 // frequency are specified at the beginning.
10 //
11
12 #include <stdio.h>
13 #include <math.h>
14 #include <complex.h>
15
16 #include "liquid.h"
17
18 #define OUTPUT_FILENAME "iirfilt_crcf_example.m"
19
main()20 int main() {
21 // options
22 unsigned int order = 4; // filter order
23 float fc = 0.1f; // cutoff frequency
24 float f0 = 0.0f; // center frequency
25 float Ap = 1.0f; // pass-band ripple
26 float As = 40.0f; // stop-band attenuation
27 unsigned int n = 128; // number of samples
28 liquid_iirdes_filtertype ftype = LIQUID_IIRDES_ELLIP;
29 liquid_iirdes_bandtype btype = LIQUID_IIRDES_LOWPASS;
30 liquid_iirdes_format format = LIQUID_IIRDES_SOS;
31
32 // design filter from prototype
33 iirfilt_crcf q = iirfilt_crcf_create_prototype(
34 ftype, btype, format, order, fc, f0, Ap, As);
35 iirfilt_crcf_print(q);
36
37 unsigned int i;
38
39 // allocate memory for data arrays
40 float complex x[n];
41 float complex y[n];
42
43 // generate input signal (noisy sine wave with decaying amplitude)
44 for (i=0; i<n; i++) {
45 x[i] = cexpf((2*M_PI*0.057f*_Complex_I - 0.04f)*i);
46 x[i] += 0.1f*(randnf() + _Complex_I*randnf());
47
48 // run filter
49 iirfilt_crcf_execute(q, x[i], &y[i]);
50 }
51
52 // compute response
53 unsigned int nfft=512;
54 float complex H[nfft];
55 for (i=0; i<nfft; i++) {
56 float freq = 0.5f * (float)i / (float)nfft;
57 iirfilt_crcf_freqresponse(q, freq, &H[i]);
58 }
59
60 // destroy filter object
61 iirfilt_crcf_destroy(q);
62
63 //
64 // plot results to output file
65 //
66 FILE * fid = fopen(OUTPUT_FILENAME,"w");
67 fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
68 fprintf(fid,"clear all;\n");
69 fprintf(fid,"close all;\n");
70 fprintf(fid,"\n");
71 fprintf(fid,"order=%u;\n", order);
72 fprintf(fid,"n=%u;\n",n);
73 fprintf(fid,"nfft=%u;\n",nfft);
74 fprintf(fid,"x=zeros(1,n);\n");
75 fprintf(fid,"y=zeros(1,n);\n");
76 fprintf(fid,"H=zeros(1,nfft);\n");
77
78 for (i=0; i<n; i++) {
79 //printf("%4u : %12.8f + j*%12.8f\n", i, crealf(y), cimagf(y));
80 fprintf(fid,"x(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
81 fprintf(fid,"y(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
82 }
83
84 for (i=0; i<nfft; i++)
85 fprintf(fid,"H(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(H[i]), cimagf(H[i]));
86
87 // plot output
88 fprintf(fid,"t=0:(n-1);\n");
89 fprintf(fid,"figure;\n");
90 fprintf(fid,"subplot(2,1,1);\n");
91 fprintf(fid," plot(t,real(x),'-','Color',[1 1 1]*0.5,'LineWidth',1,...\n");
92 fprintf(fid," t,real(y),'-','Color',[0 0.5 0.25],'LineWidth',2);\n");
93 fprintf(fid," xlabel('time');\n");
94 fprintf(fid," ylabel('real');\n");
95 fprintf(fid," legend('input','filtered output','location','northeast');\n");
96 fprintf(fid," grid on;\n");
97 fprintf(fid,"subplot(2,1,2);\n");
98 fprintf(fid," plot(t,imag(x),'-','Color',[1 1 1]*0.5,'LineWidth',1,...\n");
99 fprintf(fid," t,imag(y),'-','Color',[0 0.25 0.5],'LineWidth',2);\n");
100 fprintf(fid," xlabel('time');\n");
101 fprintf(fid," ylabel('imag');\n");
102 fprintf(fid," legend('input','filtered output','location','northeast');\n");
103 fprintf(fid," grid on;\n");
104
105 // plot frequency response
106 fprintf(fid,"f=0.5*[0:(nfft-1)]/nfft;\n");
107 fprintf(fid,"figure;\n");
108 fprintf(fid,"subplot(3,1,1);\n");
109 fprintf(fid," plot(f,20*log10(abs(H)),'Color',[0 0.25 0.5],'LineWidth',2);\n");
110 fprintf(fid," axis([0 0.5 -3 0]);\n");
111 fprintf(fid," grid on;\n");
112 fprintf(fid," ylabel('Pass band [dB]');\n");
113 fprintf(fid,"subplot(3,1,2);\n");
114 fprintf(fid," plot(f,20*log10(abs(H)),'Color',[0 0.25 0.5],'LineWidth',2);\n");
115 fprintf(fid," axis([0 0.5 -100 0]);\n");
116 fprintf(fid," grid on;\n");
117 fprintf(fid," ylabel('Stop band [dB]');\n");
118 fprintf(fid,"subplot(3,1,3);\n");
119 fprintf(fid," plot(f,180/pi*arg(H),'Color',[0 0.25 0.5],'LineWidth',2);\n");
120 //fprintf(fid," axis([0 0.5 -100 0]);\n");
121 fprintf(fid," grid on;\n");
122 fprintf(fid," ylabel('Phase [degrees]');\n");
123 fprintf(fid," xlabel('Normalized Frequency [f/F_s]');\n");
124 fclose(fid);
125 printf("results written to %s.\n", OUTPUT_FILENAME);
126
127 printf("done.\n");
128 return 0;
129 }
130
131