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//
// spgramf_example.c
//
// Spectral periodogram example with real inputs.
//
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include "liquid.h"
#define OUTPUT_FILENAME "spgramf_example.m"
int main() {
// spectral periodogram options
unsigned int nfft = 1024; // spectral periodogram FFT size
unsigned int num_samples = 1e6; // number of samples
float noise_floor = -60.0f; // noise floor [dB]
unsigned int i;
// derived values
float nstd = powf(10.0f, noise_floor/20.0f);
// create spectral periodogram
spgramf q = spgramf_create_default(nfft);
spgramf_print(q);
// generate signal (band-pass filter)
iirfilt_rrrf filter = iirfilt_rrrf_create_prototype(
LIQUID_IIRDES_BUTTER,
LIQUID_IIRDES_BANDPASS,
LIQUID_IIRDES_SOS,
9, 0.17f, 0.20f, 0.1f, 60.0f);
for (i=0; i<num_samples; i++) {
// filter input noise signal
float y = 0;
iirfilt_rrrf_execute(filter, randnf(), &y);
// add noise
y += nstd * randnf();
// push resulting sample through periodogram
spgramf_push(q, y);
}
// compute power spectral density output
float psd[nfft];
spgramf_get_psd(q, psd);
// destroy objects
iirfilt_rrrf_destroy(filter);
spgramf_destroy(q);
//
// export 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,"nfft = %u;\n", nfft);
fprintf(fid,"f = [0:(nfft-1)]/nfft - 0.5;\n");
fprintf(fid,"H = zeros(1,nfft);\n");
fprintf(fid,"noise_floor = %12.6f;\n", noise_floor);
for (i=0; i<nfft; i++)
fprintf(fid,"H(%6u) = %12.4e;\n", i+1, psd[i]);
fprintf(fid,"figure;\n");
fprintf(fid,"plot(f, H, '-', 'LineWidth',1.5);\n");
fprintf(fid,"xlabel('Normalized Frequency [f/F_s]');\n");
fprintf(fid,"ylabel('Power Spectral Density [dB]');\n");
fprintf(fid,"grid on;\n");
fprintf(fid,"ymin = 10*floor([noise_floor-20]/10);\n");
fprintf(fid,"ymax = 10*floor([noise_floor+80]/10);\n");
fprintf(fid,"axis([-0.5 0.5 ymin ymax]);\n");
fclose(fid);
printf("results written to %s.\n", OUTPUT_FILENAME);
printf("done.\n");
return 0;
}
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