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//
// iirfilt_cccf_example.c
//
// Complex infinite impulse response filter example. Demonstrates the
// functionality of iirfilt with complex coefficients by designing a
// filter with specified parameters and then filters noise.
//
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <math.h>
#include <complex.h>
#include <getopt.h>
#include "liquid.h"
#define OUTPUT_FILENAME "iirfilt_cccf_example.m"
// print usage/help message
void usage()
{
printf("iirfilt_cccf_example -- infinite impulse response filter example\n");
printf("options (default values in []):\n");
printf(" h : print help\n");
printf(" t : filter type: [butter], cheby1, cheby2, ellip, bessel\n");
printf(" b : filter transformation: [LP], HP, BP, BS\n");
printf(" n : filter order, n > 0 [5]\n");
printf(" r : passband ripple in dB (cheby1, ellip), r > 0 [1.0]\n");
printf(" s : stopband attenuation in dB (cheby2, ellip), s > 0 [40.0]\n");
printf(" f : passband cut-off, 0 < f < 0.5 [0.2]\n");
printf(" c : center frequency (BP, BS cases), 0 < c < 0.5 [0.25]\n");
printf(" o : format [sos], tf\n");
printf(" sos : second-order sections form\n");
printf(" tf : regular transfer function form (potentially\n");
printf(" unstable for large orders\n");
}
int main(int argc, char*argv[])
{
// options
unsigned int order=4; // filter order
float fc=0.1f; // cutoff frequency
float f0=0.0f; // center frequency
float Ap=1.0f; // pass-band ripple
float As=40.0f; // stop-band attenuation
unsigned int n=128; // number of samples
liquid_iirdes_filtertype ftype = LIQUID_IIRDES_ELLIP;
liquid_iirdes_bandtype btype = LIQUID_IIRDES_LOWPASS;
liquid_iirdes_format format = LIQUID_IIRDES_SOS;
int dopt;
while ((dopt = getopt(argc,argv,"ht:b:n:r:s:f:c:o:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 't':
if (strcmp(optarg,"butter")==0) ftype = LIQUID_IIRDES_BUTTER;
else if (strcmp(optarg,"cheby1")==0) ftype = LIQUID_IIRDES_CHEBY1;
else if (strcmp(optarg,"cheby2")==0) ftype = LIQUID_IIRDES_CHEBY2;
else if (strcmp(optarg,"ellip") ==0) ftype = LIQUID_IIRDES_ELLIP;
else if (strcmp(optarg,"bessel")==0) ftype = LIQUID_IIRDES_BESSEL;
else {
fprintf(stderr,"error: iirdes_example, unknown filter type '%s'\n", optarg);
exit(1);
}
break;
case 'b':
if (strcmp(optarg,"LP")==0) btype = LIQUID_IIRDES_LOWPASS;
else if (strcmp(optarg,"HP")==0) btype = LIQUID_IIRDES_HIGHPASS;
else if (strcmp(optarg,"BP")==0) btype = LIQUID_IIRDES_BANDPASS;
else if (strcmp(optarg,"BS")==0) btype = LIQUID_IIRDES_BANDSTOP;
else {
fprintf(stderr,"error: iirdes_example, unknown band type '%s'\n", optarg);
exit(1);
}
break;
case 'n': order = atoi(optarg); break;
case 'r': Ap = atof(optarg); break;
case 's': As = atof(optarg); break;
case 'f': fc = atof(optarg); break;
case 'c': f0 = atof(optarg); break;
case 'o':
if (strcmp(optarg,"sos")==0) format = LIQUID_IIRDES_SOS;
else if (strcmp(optarg,"tf") ==0) format = LIQUID_IIRDES_TF;
else {
fprintf(stderr,"error: iirdes_example, unknown output format '%s'\n", optarg);
exit(1);
}
break;
default:
exit(1);
}
}
// design filter from prototype
iirfilt_cccf q = iirfilt_cccf_create_prototype(ftype, btype, format, order, fc, f0, Ap, As);
iirfilt_cccf_print(q);
unsigned int i;
// allocate memory for data arrays
float complex x[n];
float complex y[n];
// generate input signal (noisy sine wave with decaying amplitude)
unsigned int wlen = (3*n)/4;
for (i=0; i<n; i++) {
// input signal (windowed noise)
x[i] = randnf() + _Complex_I*randnf();
x[i] *= i < wlen ? liquid_hamming(i,wlen) : 0.0f;
// run filter
iirfilt_cccf_execute(q, x[i], &y[i]);
}
// compute two-sided frequency response
unsigned int nfft=512;
float complex H[nfft];
for (i=0; i<nfft; i++) {
float freq = (float)i / (float)nfft - 0.5f;
iirfilt_cccf_freqresponse(q, freq, &H[i]);
}
// destroy filter object
iirfilt_cccf_destroy(q);
//
// plot results to output file
//
FILE * fid = fopen(OUTPUT_FILENAME,"w");
fprintf(fid,"%% %s : auto-generated file\n", OUTPUT_FILENAME);
fprintf(fid,"clear all;\n");
fprintf(fid,"close all;\n");
fprintf(fid,"\n");
fprintf(fid,"order=%u;\n", order);
// save input, output arrays
fprintf(fid,"n=%u;\n",n);
fprintf(fid,"x=zeros(1,n);\n");
fprintf(fid,"y=zeros(1,n);\n");
for (i=0; i<n; i++) {
fprintf(fid,"x(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(x[i]), cimagf(x[i]));
fprintf(fid,"y(%4u) = %12.4e + j*%12.4e;\n", i+1, crealf(y[i]), cimagf(y[i]));
}
// save frequency response
fprintf(fid,"nfft=%u;\n",nfft);
fprintf(fid,"H=zeros(1,nfft);\n");
for (i=0; i<nfft; i++)
fprintf(fid,"H(%4u) = %12.8f + j*%12.8f;\n", i+1, crealf(H[i]), cimagf(H[i]));
// plot time-domain output
fprintf(fid,"t=0:(n-1);\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(2,1,1);\n");
fprintf(fid," plot(t,real(x),'-','Color',[1 1 1]*0.5,'LineWidth',1,...\n");
fprintf(fid," t,real(y),'-','Color',[0 0.5 0.25],'LineWidth',2);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('real');\n");
fprintf(fid," legend('input','filtered output',1);\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(2,1,2);\n");
fprintf(fid," plot(t,imag(x),'-','Color',[1 1 1]*0.5,'LineWidth',1,...\n");
fprintf(fid," t,imag(y),'-','Color',[0 0.25 0.5],'LineWidth',2);\n");
fprintf(fid," xlabel('time');\n");
fprintf(fid," ylabel('imag');\n");
fprintf(fid," legend('input','filtered output',1);\n");
fprintf(fid," grid on;\n");
// plot spectral output
fprintf(fid,"X = 20*log10(abs(fftshift(fft(x))));\n");
fprintf(fid,"Y = 20*log10(abs(fftshift(fft(y))));\n");
fprintf(fid,"figure;\n");
fprintf(fid,"plot([0:(n-1)]/n-0.5, X, 'Color', [1 1 1]*0.5,\n");
fprintf(fid," [0:(n-1)]/n-0.5, Y, 'Color', [0 0.25 0.50]);\n");
fprintf(fid,"xlabel('Normalized Frequency');\n");
fprintf(fid,"ylabel('PSD [dB]');\n");
fprintf(fid,"legend('input','filtered output',1);\n");
fprintf(fid,"grid on;\n");
// plot ideal frequency response
fprintf(fid,"f=[0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(3,1,1);\n");
fprintf(fid," plot(f,20*log10(abs(H)));\n");
fprintf(fid," axis([-0.5 0.5 -3 0]);\n");
fprintf(fid," grid on;\n");
fprintf(fid," legend('Pass band (dB)',0);\n");
fprintf(fid,"subplot(3,1,2);\n");
fprintf(fid," plot(f,20*log10(abs(H)));\n");
fprintf(fid," axis([-0.5 0.5 -100 0]);\n");
fprintf(fid," grid on;\n");
fprintf(fid," legend('Stop band (dB)',0);\n");
fprintf(fid,"subplot(3,1,3);\n");
fprintf(fid," plot(f,180/pi*arg(H));\n");
fprintf(fid," axis([-0.5 0.5 -180 180]);\n");
fprintf(fid," grid on;\n");
fprintf(fid," legend('Phase (degrees)',0);\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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