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//
// firhilb_filter_example.c
//
// Hilbert transform example. This example demonstrates the
// functionality of firhilbf (finite impulse response Hilbert transform)
// as a filter to remove the negative half of the spectrum.
//
// SEE ALSO: firhilb_interp_example.c
// firhilb_example.c
//
#include <stdio.h>
#include <complex.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "firhilb_filter_example.m"
int main() {
unsigned int m = 7; // Hilbert filter semi-length
float As = 60.0f; // stop-band attenuation [dB]
unsigned int n = 128; // number of input samples
int usb = 1; // keep upper (or lower) side-band
// derived values
unsigned int h_len = 4*m+1; // filter length
unsigned int num_samples = n + h_len;
// create Hilbert transform object
firhilbf q0 = firhilbf_create(m,As); // interpolator
firhilbf q1 = firhilbf_create(m,As); // decimator
firhilbf_print(q0);
// data arrays
float complex x[num_samples]; // complex input
float y[num_samples]; // real output
float complex z[num_samples]; // complex output
// run transform
unsigned int i;
for (i=0; i<num_samples; i++) {
// generate input
x[i] = 1.0f*cexpf( 0.12f*_Complex_I*2*M_PI*i) + // primary tone
0.1f*cexpf( 0.17f*_Complex_I*2*M_PI*i) + // secondary tone
0.2f*cexpf(-0.40f*_Complex_I*2*M_PI*i); // tone in negative spectrum
x[i] *= (i < n) ? 1.855f*liquid_hamming(i,n) : 0.0f;
// convert to real
float y0, y1;
firhilbf_c2r_execute(q0, x[i], &y0, &y1);
y[i] = usb ? y1 : y0;
// convert back to complex
firhilbf_r2c_execute(q1, y[i], &z[i]);
}
// destroy Hilbert transform object
firhilbf_destroy(q0);
firhilbf_destroy(q1);
//
// export results to 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,"h_len=%u;\n", 4*m+1);
fprintf(fid,"n=%u;\n", n);
fprintf(fid,"num_samples=%u;\n", num_samples);
fprintf(fid,"t = 0:(num_samples-1);\n");
for (i=0; i<num_samples; i++) {
// print results
fprintf(fid,"x(%3u) = %12.4e + %12.4ej;\n", i+1, crealf(x[i]), cimagf(x[i]));
fprintf(fid,"y(%3u) = %12.4e;\n", i+1, y[i]);
fprintf(fid,"z(%3u) = %12.4e + %12.4ej;\n", i+1, crealf(z[i]), cimagf(z[i]));
}
fprintf(fid,"figure;\n");
fprintf(fid,"subplot(3,1,1);\n");
fprintf(fid," plot(t,real(x),'Color',[0.00 0.25 0.50],'LineWidth',1.3,...\n");
fprintf(fid," t,imag(x),'Color',[0.00 0.50 0.25],'LineWidth',1.3);\n");
fprintf(fid," legend('real','imag','location','northeast');\n");
fprintf(fid," ylabel('transformed/complex');\n");
fprintf(fid," axis([0 num_samples -2 2]);\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,1,2);\n");
fprintf(fid," plot(t,y/2,'Color',[0.00 0.25 0.50],'LineWidth',1.3);\n");
fprintf(fid," ylabel('original/real');\n");
fprintf(fid," axis([0 num_samples -2 2]);\n");
fprintf(fid," grid on;\n");
fprintf(fid,"subplot(3,1,3);\n");
fprintf(fid," plot(t,real(z)/2,'Color',[0.00 0.25 0.50],'LineWidth',1.3,...\n");
fprintf(fid," t,imag(z)/2,'Color',[0.00 0.50 0.25],'LineWidth',1.3);\n");
fprintf(fid," legend('real','imag','location','northeast');\n");
fprintf(fid," ylabel('transformed/complex');\n");
fprintf(fid," axis([0 num_samples -2 2]);\n");
fprintf(fid," grid on;\n");
// plot results
fprintf(fid,"nfft=4096;\n");
fprintf(fid,"%% compute normalized windowing functions\n");
fprintf(fid,"X=20*log10(abs(fftshift(fft( x/n,nfft))));\n");
fprintf(fid,"Y=20*log10(abs(fftshift(fft( y/n,nfft))));\n");
fprintf(fid,"Z=20*log10(abs(fftshift(fft(0.5*z/n,nfft))));\n");
fprintf(fid,"f =[0:(nfft-1)]/nfft-0.5;\n");
fprintf(fid,"figure('position',[100 100 600 800]);\n");
fprintf(fid,"subplot(3,1,1),\n");
fprintf(fid," plot(f,X); axis([-0.5 0.5 -60 5]); grid on; ylabel('original/cplx');\n");
fprintf(fid,"subplot(3,1,2),\n");
fprintf(fid," plot(f,Y); axis([-0.5 0.5 -60 5]); grid on; ylabel('transformed/real');\n");
fprintf(fid,"subplot(3,1,3),\n");
fprintf(fid," plot(f,Z); axis([-0.5 0.5 -60 5]); grid on; ylabel('regenerated/cplx');\n");
fprintf(fid," xlabel('Normalized Frequency [f/F_s]');\n");
fclose(fid);
printf("results written to %s\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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