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//
// firdespm_callback_example.c
//
// This example demonstrates finite impulse response filter design
// using the Parks-McClellan algorithm with callback function for
// arbitrary response and weighting function.
//
// SEE ALSO: firdes_kaiser_example.c
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "firdespm_callback_example.m"
// user-defined callback function defining response and weights
int callback(double _frequency,
void * _userdata,
double * _desired,
double * _weight)
{
// de-reference pointer as floating-point value
unsigned int n = *((unsigned int*)_userdata);
double v = sincf(n*_frequency);
double fc = 1.0f / (float)n;
// inverse sinc
if (_frequency < fc) {
*_desired = 1.0f / v; // inverse of sinc
*_weight = 4.0f;
} else {
*_desired = 0.0f; // stop-band
*_weight = 10*fabs(v) * exp(4.0*_frequency);
}
return 0;
}
int main(int argc, char*argv[])
{
// filter design parameters
unsigned int n = 8; // sinc filter length
unsigned int h_len = 81; // inverse sinc filter length
liquid_firdespm_btype btype = LIQUID_FIRDESPM_BANDPASS;
unsigned int num_bands = 2;
float bands[4] = {0.00f, 0.75f/(float)n, // pass-band
1.05f/(float)n, 0.5f}; // stop-band
// design filter
float h[h_len];
firdespm q = firdespm_create_callback(h_len,num_bands,bands,btype,callback,&n);
firdespm_execute(q,h);
firdespm_destroy(q);
// print coefficients
unsigned int i;
for (i=0; i<h_len; i++)
printf("h(%4u) = %16.12f;\n", i+1, h[i]);
// 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,"n=%u;\n", n);
fprintf(fid,"h_len=%u;\n", h_len);
for (i=0; i<h_len; i++)
fprintf(fid,"h(%4u) = %20.8e;\n", i+1, h[i]);
fprintf(fid,"nfft=1024;\n");
fprintf(fid,"H0=20*log10(abs(fftshift(fft(ones(1,n)/n,nfft))));\n");
fprintf(fid,"H1=20*log10(abs(fftshift(fft(h, nfft))));\n");
fprintf(fid,"Hc=H0+H1;\n");
fprintf(fid,"f=[0:(nfft-1)]/nfft-0.5;\n");
fprintf(fid,"figure;\n");
fprintf(fid,"hold on;\n");
fprintf(fid,"plot(f,H0,'Color',[0.5 0.5 0.5],'LineWidth',1);\n");
fprintf(fid,"plot(f,H1,'Color',[0.0 0.2 0.5],'LineWidth',1);\n");
fprintf(fid,"plot(f,Hc,'Color',[0.0 0.5 0.2],'LineWidth',2);\n");
fprintf(fid,"hold off;\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"xlabel('normalized frequency');\n");
fprintf(fid,"ylabel('PSD [dB]');\n");
fprintf(fid,"legend('sinc','inverse sinc','composite');\n");
fprintf(fid,"title('Filter design (firdespm), inverse sinc');\n");
fprintf(fid,"axis([-0.5 0.5 -80 20]);\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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