157 lines
3.1 KiB
C
157 lines
3.1 KiB
C
/*
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* Copyright 2022 Oleg Borodin <borodin@unix7.org>
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#include <fcntl.h>
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#include <unistd.h>
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#include <complex.h>
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typedef struct {
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double x1;
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double x2;
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double x3;
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double rc;
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} lpf_t;
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void lpf_init(lpf_t *lpf, double freq) {
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lpf->x1 = 0.0;
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lpf->x2 = 0.0;
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lpf->x3 = 0.0;
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double order = 3.0;
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double c = 1.0 / sqrt(powf(2.0, 1.0 / order) - 1.0);
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lpf->rc = 1.0 / (2.0 * c * M_PI * freq);
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}
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double lpf_apply(lpf_t *lpf, double x0, double dt) {
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double k = dt / (lpf->rc + dt);
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lpf->x1 = lpf->x1 + k * (x0 - lpf->x1);
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lpf->x2 = lpf->x2 + k * (lpf->x1 - lpf->x2);
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lpf->x3 = lpf->x3 + k * (lpf->x2 - lpf->x3);
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return lpf->x3;
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}
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void dft(double* x1, double* y1, int m, int dir) {
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long i, k;
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double arg;
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double cosarg, sinarg;
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double x2[m];
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double y2[m];
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for (i = 0; i < m; i++) {
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x2[i] = 0;
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y2[i] = 0;
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arg = -dir * 2.0 * M_PI * (double)i / (double)m;
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for (k = 0; k < m; k++) {
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cosarg = cos(k * arg);
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sinarg = sin(k * arg);
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x2[i] += (x1[k] * cosarg - y1[k] * sinarg);
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y2[i] += (x1[k] * sinarg + y1[k] * cosarg);
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}
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}
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if (dir == 1) {
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for (i = 0; i < m; i++) {
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x1[i] = x2[i] / (double)m;
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y1[i] = y2[i] / (double)m;
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}
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} else {
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for (i = 0; i < m; i++) {
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x1[i] = x2[i];
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y1[i] = y2[i];
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}
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}
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}
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int main(int argc, char** argv) {
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double t = 0;
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double s = 0;
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double freq0 = 20;
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double dt = 0.001;
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lpf_t lpf;
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lpf_init(&lpf, 20.0);
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int c = 1024 * 2;
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double xa[c];
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double xb[c];
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double y[c];
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for (int i = 0; i < c; i++) {
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t = i * dt;
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for (int n = 0; n < 200; n += 20) {
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double freq = freq0 + n;
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s += cos(2 * M_PI * freq * t);
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}
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xa[i] = s;
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xb[i] = lpf_apply(&lpf, s, dt);;
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}
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for (int i = 0; i < c; i++) {
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y[i] = 0;
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}
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double rate = 1.0 / dt;
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FILE* fd;
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fd = popen("gnuplot -persistent", "w");
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fprintf(fd, "set terminal png size 1600,1200\n");
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fprintf(fd, "set output \"gensin4a.png\"\n");
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fprintf(fd, "plot '-' with lines\n");
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dft(xa, y, c, -1);
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for (int i = 0; i < c; i++) {
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double freq = rate * (double)i / (double)c;
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double amp = sqrt(xa[i] * xa[i] + y[i] * y[i]);
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if (freq < rate / 2) {
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fprintf(fd, "%e %e\n", freq, amp);
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}
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}
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fflush(fd);
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fprintf(fd, "e");
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fclose(fd);
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for (int i = 0; i < c; i++) {
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y[i] = 0;
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}
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fd = popen("gnuplot -persistent", "w");
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fprintf(fd, "set terminal png size 1600,1200\n");
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fprintf(fd, "set output \"gensin4b.png\"\n");
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fprintf(fd, "plot '-' with lines\n");
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dft(xb, y, c, -1);
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for (int i = 0; i < c; i++) {
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double freq = rate * (double)i / (double)c;
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double amp = sqrt(xb[i] * xb[i] + y[i] * y[i]);
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if (freq < rate / 2) {
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fprintf(fd, "%e %e\n", freq, amp);
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}
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}
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fflush(fd);
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fprintf(fd, "e");
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fclose(fd);
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return 0;
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}
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