using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace Spectrogram

{

public static class Operations

{

public enum WindowFunction { none, hanning, triangle };

public static bool IsPowerOfTwo(int number)

{

for (int i = 0; i < 20; i++)

{

int powerOfTwo = (1 << i);

if (number == powerOfTwo)

return true;

else if (powerOfTwo > number)

return false;

}

return false;

}

public static double TriangleWindow(int n, int frameSize)

{

int pointsFromCenter = Math.Abs(frameSize / 2 - n);

int pointsFromEdge = frameSize / 2 - pointsFromCenter;

double fractionFromEdge = (double)pointsFromEdge / (frameSize / 2);

return fractionFromEdge;

}

public static float[] FFT(float[] values, WindowFunction window = WindowFunction.hanning)

{

int fftSize = values.Length;

if (!IsPowerOfTwo(fftSize))

throw new ArgumentException("FFT Size must be a power of 2");

NAudio.Dsp.Complex[] fft_buffer = new NAudio.Dsp.Complex[fftSize];

for (int i = 0; i < fftSize; i++)

{

fft_buffer[i].X = (float)values[i];

fft_buffer[i].Y = 0;

switch (window)

{

case WindowFunction.none:

break;

case WindowFunction.hanning:

fft_buffer[i].X *= (float)NAudio.Dsp.FastFourierTransform.HammingWindow(i, fftSize);

break;

case WindowFunction.triangle:

fft_buffer[i].X *= (float)TriangleWindow(i, fftSize);

break;

default:

throw new NotImplementedException("unsupported window function");

}

}

NAudio.Dsp.FastFourierTransform.FFT(true, (int)Math.Log(fftSize, 2.0), fft_buffer);

float[] fft = new float[fftSize / 2];

for (int i = 0; i < fft.Length; i++)

{

var fftL = fft_buffer[i];

var fftR = fft_buffer[fft_buffer.Length - i - 1];

// note that this is different than just taking the absolute value

float absL = (float)Math.Sqrt(fftL.X * fftL.X + fftL.Y * fftL.Y);

float absR = (float)Math.Sqrt(fftR.X * fftR.X + fftR.Y * fftR.Y);

fft[i] = (absL + absR) / 2;

}

return fft;

}

}

}