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fourier.cpp
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fourier.cpp
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#include <math.h>
#include <stdlib.h>
#include <stdio.h>
#include "fourier.h"
#include <iostream>
/* alpha = RC / (RC + dt)
* cutoff frequency propto 1/RC
*
* RC = 1 / f
* dt = 1 / rate
* So alpha should be (rate / f) / ( rate / f + 1 / rate )
**/
void lowpass(double x[], int length, double frq, double rate) {
double alpha = (1 / frq) / ( (1 / frq) + 1 / rate );
int i;
for(i = 1; i < length; i++) {
x[i] = alpha * x[i] + (1 - alpha)* x[i-1];
}
}
void highpass(double x[], int length, double frq, double rate) {
double alpha = (1 / frq) / ( (1 / frq) + 1 / rate );
int i;
double y[length];
y[0] = x[0];
for(i = 1; i < length; i++) {
y[i] = alpha * (y[i-1] + x[i] - x[i-1]);
}
for(i = 0; i < length; i++) {
x[i] = y[i];
}
}
double fourier1(double x_in[], double n, int length) {
double x_complex[2] = { 0, 0 };
int i;
for(i = 0; i < length; i++) {
x_complex[0] += x_in[i] * cos(M_PI * 2 * i * n / (double) length);
x_complex[1] += x_in[i] * sin(M_PI * 2 * i * n / (double) length);
}
return sqrt(x_complex[0]*x_complex[0] + x_complex[1]*x_complex[1]) / (double) length;
}
double fourier1p(double x_in[], double n, int length, double* phase_r, double* phase_i) {
double x_complex[2] = { 0, 0 };
int i;
for(i = 0; i < length; i++) {
x_complex[0] += x_in[i] * cos(M_PI * 2 * i * n / (double) length);
x_complex[1] += x_in[i] * sin(M_PI * 2 * i * n / (double) length);
}
double norm = sqrt(x_complex[0]*x_complex[0] + x_complex[1]*x_complex[1]);
*phase_i = x_complex[1] / norm;
*phase_r = x_complex[0] / norm;
return norm / length;
}
void fourier_w(double x_in[], double x_out[], int length) {
int i;
for(i = 0; i < length; i++) {
x_out[i] = fourier1(x_in, i, length);
}
}
void fourier_xpm_start(int seg_length, int file_length, FILE* output) {
int i;
fprintf(output, "! XPM2\n");
fprintf(output,"%d %d 256 2\n", seg_length, file_length);
for(i = 0; i < 256; i++) {
fprintf(output, "%2.2x c #%2.2x%2.2x%2.2x\n", i, i, i, i);
}
}
void fourier_xpm_line(double x_in[], int length, FILE* output) {
int i;
double x_out[length];
fourier_w(x_in, x_out, length);
for(i = 0; i < length; i++) {
fprintf(output, "%2.2x", (unsigned char) (256 * x_out[i]));
}
fprintf(output, "\n");
}
void blackman_harris(double *data, int numSamples)
{
for (int n=0; n<numSamples; n++)
{
data[n] *= (double) 0.35875 - 0.48829*cos( 2*M_PI*n/(numSamples-1) ) + 0.14128*cos( 4*M_PI*n/(numSamples-1) ) - 0.01168*cos( 6*M_PI*n/(numSamples-1) );
}
}
void hanning(double *data, int numSamples)
{
for (int n=0; n<numSamples; n++)
{
data[n] *= (double) 0.5 * ( 1-cos( 2*M_PI*n/(numSamples-1) ) );
}
}
void my_filter(double *data, int numSamples)
{
for (int n=0; n<numSamples/5; n++)
{
data[n] *= (double) n/(numSamples/5.0);
data[numSamples-n-1] *= (double) n/(numSamples/5.0);
}
}
double goertzel_mag(int numSamples,int TARGET_FREQUENCY,int SAMPLING_RATE, double* data)
{
int k,i;
double floatnumSamples;
double omega,sine,cosine,coeff,q0,q1,q2,real,imag;
double scalingFactor = numSamples / 2.0;
floatnumSamples = (double) numSamples;
k = (int) (0.5 + ((floatnumSamples * TARGET_FREQUENCY) / SAMPLING_RATE));
omega = (2.0 * M_PI * k) / floatnumSamples;
sine = sin(omega);
cosine = cos(omega);
coeff = 2.0 * cosine;
q0=0;
q1=0;
q2=0;
// my_filter(data, numSamples);
for(i=0; i<numSamples; i++)
{
q0 = coeff * q1 - q2 + data[i];
q2 = q1;
q1 = q0;
}
// calculate the real and imaginary results
// scaling appropriately
real = (q1 - q2 * cosine) / scalingFactor;
imag = (q2 * sine) / scalingFactor;
return sqrtf(real*real + imag*imag);
}
unsigned int zeroX(short *data, unsigned int length)
{
unsigned int counter=0;
short lastSample = data[0];
for (unsigned int i=1; i<length; i++)
{
if ( data[i] )
{
if ( lastSample*data[i]<0 ) counter++;
lastSample = data[i];
}
}
return counter;
}