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//
// firdespm_lowpass_example.c
//
// This example demonstrates a low-pass finite impulse response filter
// design using the Parks-McClellan algorithm.
//
// SEE ALSO: firdes_kaiser_example.c
#include <stdio.h>
#include <stdlib.h>
#include <getopt.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "firdespm_lowpass_example.m"
// print usage/help message
void usage()
{
printf("firdespm_lowpass_example:\n");
printf(" -h : print usage/help\n");
printf(" -n <len> : filter length, 1 < n default: 57\n");
printf(" -f <freq> : filter cutoff frequency, 0 < f < 0.5, default: 0.2\n");
printf(" -s <atten>: stop-band attenuation [dB], 0 < s, default: 60\n");
}
int main(int argc, char*argv[]) {
// options
unsigned int n = 57; // filter cutoff frequency
float fc = 0.2f; // filter cutoff frequency
float As = 60.0f; // stop-band attenuation [dB]
int dopt;
while ((dopt = getopt(argc,argv,"hn:f:s:")) != EOF) {
switch (dopt) {
case 'h': usage(); return 0;
case 'n': n = atoi(optarg); break;
case 'f': fc = atof(optarg); break;
case 's': As = atof(optarg); break;
default: return -1;
}
}
unsigned int i;
printf("filter design parameters\n");
printf(" length : %12u\n", n);
printf(" cutoff frequency : %12.8f Fs\n", fc);
printf(" stop-band attenuation : %12.3f dB\n", As);
// design the filter
float h[n];
firdespm_lowpass(n,fc,As,0,h);
#if 0
// print coefficients
for (i=0; i<n; i++)
printf("h(%4u) = %16.12f;\n", i+1, h[i]);
#endif
// open 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\n");
fprintf(fid,"h_len=%u;\n", n);
fprintf(fid,"fc=%12.4e;\n",fc);
fprintf(fid,"As=%12.4e;\n",As);
for (i=0; i<n; i++)
fprintf(fid,"h(%4u) = %20.8e;\n", i+1, h[i]);
fprintf(fid,"nfft=1024;\n");
fprintf(fid,"H=20*log10(abs(fftshift(fft(h,nfft))));\n");
fprintf(fid,"f=[0:(nfft-1)]/nfft-0.5;\n");
fprintf(fid,"figure; plot(f,H,'Color',[0 0.5 0.25],'LineWidth',2);\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"xlabel('normalized frequency');\n");
fprintf(fid,"ylabel('PSD [dB]');\n");
fprintf(fid,"title(['Filter design (firdespm) f_c: %.3f, S_L: %.3f, h: %u']);\n",
fc, -As, n);
fprintf(fid,"axis([-0.5 0.5 -As-20 10]);\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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