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// ASCII spectrogram example for real-valued input. This example demonstrates
// the functionality of the ASCII spectrogram for real-valued input siganls.
// A cosine signal with time-varying frequency is generated and the resulting
// spectral periodogram is printed to the screen. Because the time signal has
// no complex component, its spectrum is symmetric.
#include <unistd.h> // usleep
#include <stdio.h>
#include <math.h>
#include "liquid.h"
int main() {
// options
unsigned int nfft = 64; // transform size
unsigned int num_frames = 200; // total number of frames
unsigned int msdelay = 25; // delay between transforms [ms]
float noise_floor = -40.0f; // noise floor
// initialize objects
asgramf q = asgramf_create(nfft);
asgramf_set_scale(q, noise_floor+15.0f, 5.0f);
unsigned int i;
unsigned int n;
float theta = 0.0f; // current instantaneous phase
float dtheta = 0.0f; // current instantaneous frequency
float phi = 0.0f; // phase of sinusoidal frequency drift
float dphi = 0.003f; // frequency of sinusoidal frequency drift
float nstd = powf(10.0f,noise_floor/20.0f); // noise standard deviation
for (n=0; n<num_frames; n++) {
// generate a frame of data samples
for (i=0; i<nfft; i++) {
// cosine wave of time-varying frequency with noise
float x = cosf(theta) + nstd*randnf();
// push sample into spectrogram object
asgramf_push(q, x);
// adjust frequency and phase
theta += dtheta;
dtheta = 0.5f*M_PI + 0.4f*M_PI*sinf(phi) * liquid_hamming(n, num_frames);
phi += dphi;
}
// print the spectrogram to stdout
asgramf_print(q);
// sleep for some time before generating the next frame
usleep(msdelay*1000);
}
asgramf_destroy(q);
printf("done.\n");
return 0;
}
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