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J.D. Purcell 2015-09-01 16:05:20 -04:00
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libse/Fourier.cs
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using System;
namespace Nikse.SubtitleEdit.Core
{
/// <summary>
/// Fourier transform
///
/// *****************************************************************************
/// *
/// * Copyright (c) 2002, Wilhelm Kurz. All Rights Reserved.
/// * wkurz@foni.net
/// *
/// * This file is provided for demonstration and educational uses only.
/// * Permission to use, copy, modify and distribute this file for
/// * any purpose and without fee is hereby granted.
/// *
/// *****************************************************************************
/// Converted/optimized by Nikse from vb code: http://www.wilhelm-kurz-software.de/dynaplot/applicationnotes/spectrogram.htm
/// </summary>
internal class Fourier
{
public const double W0Hanning = 0.5;
public const double W0Hamming = 0.54;
public const double W0Blackman = 0.42;
private const double Pi = 3.14159265358979;
private double[] cosarray;
private double[] sinarray;
private bool _forward;
private int _arraySize;
private int _ldArraysize = 0;
public Fourier(int arraySize, bool forward)
{
_arraySize = arraySize;
_forward = forward;
cosarray = new double[arraySize];
sinarray = new double[arraySize];
double sign = 1.0;
if (forward)
sign = -1.0;
double phase0 = 2.0 * Pi / arraySize;
for (int i = 0; i <= arraySize - 1; i++)
{
sinarray[i] = sign * Math.Sin(phase0 * i);
cosarray[i] = Math.Cos(phase0 * i);
}
int j = _arraySize;
while (j != 1)
{
_ldArraysize++;
j /= 2;
}
}
public void MagnitudeSpectrum(double[] real, double[] imag, double w0, double[] magnitude)
{
int i;
magnitude[0] = Math.Sqrt(SquareSum(real[0], imag[0]));
for (i = 1; i <= (_arraySize / 2 - 1); i++)
magnitude[i] = (Math.Sqrt(SquareSum(real[i], imag[i]) + SquareSum(real[_arraySize - i], imag[_arraySize - i]))) / w0;
}
public static double Hanning(int n, int j)
{
return W0Hanning - 0.5 * Math.Cos(2.0 * Pi * j / n);
}
public static double Hamming(int n, int j)
{
return W0Hamming - 0.46 * Math.Cos(2.0 * Pi * j / n);
}
public static double Blackman(int n, int j)
{
return W0Blackman - 0.5 * Math.Cos(2.0 * Pi * j / n) + 0.08 * Math.Cos(4.0 * Pi * j / n);
}
private static void Swap(ref double a, ref double b)
{
double temp = a;
a = b;
b = temp;
}
private static double SquareSum(double a, double b)
{
return a * a + b * b;
}
public void FourierTransform(double[] real, double[] imag)
{
int i;
if (_forward)
{
for (i = 0; i <= _arraySize - 1; i++)
{
real[i] /= _arraySize;
imag[i] /= _arraySize;
}
}
int k;
int j = 0;
for (i = 0; i <= _arraySize - 2; i++)
{
if (i < j)
{
Swap(ref real[i], ref real[j]);
Swap(ref imag[i], ref imag[j]);
}
k = _arraySize / 2;
while (k <= j)
{
j -= k;
k /= 2;
}
j += k;
}
int a = 2;
int b = 1;
for (int count = 1; count <= _ldArraysize; count++)
{
int c0 = _arraySize / a;
int c1 = 0;
for (k = 0; k <= b - 1; k++)
{
i = k;
while (i < _arraySize)
{
int arg = i + b;
double prodreal;
double prodimag;
if (k == 0)
{
prodreal = real[arg];
prodimag = imag[arg];
}
else
{
prodreal = real[arg] * cosarray[c1] - imag[arg] * sinarray[c1];
prodimag = real[arg] * sinarray[c1] + imag[arg] * cosarray[c1];
}
real[arg] = real[i] - prodreal;
imag[arg] = imag[i] - prodimag;
real[i] += prodreal;
imag[i] += prodimag;
i += a;
}
c1 += c0;
}
a *= 2;
b *= 2;
}
}
}
}