/// <summary>
/// Linear Convolution x ** h を計算。
/// </summary>
/// <param name="h">コンボリューションカーネル。左右反転される。</param>
/// <param name="x">入力数列。</param>
public WWComplex[] ConvolutionFft(WWComplex[] h, WWComplex[] x) {
var r = new WWComplex[h.Length + x.Length - 1];
int fftSize = Functions.NextPowerOf2(r.Length);
var h2 = new WWComplex[fftSize];
Array.Copy(h, 0, h2, 0, h.Length);
for (int i = h.Length; i < h2.Length; ++i) {
h2[i] = WWComplex.Zero();
}
var x2 = new WWComplex[fftSize];
Array.Copy(x, 0, x2, 0, x.Length);
for (int i = x.Length; i < x2.Length; ++i) {
x2[i] = WWComplex.Zero();
}
var fft = new WWRadix2Fft(fftSize);
var H = fft.ForwardFft(h2);
var X = fft.ForwardFft(x2);
var Y = WWComplex.Mul(H, X);
var y = fft.InverseFft(Y);
Array.Copy(y, 0, r, 0, r.Length);
return r;
}
/// <summary>
/// 連続FFT オーバーラップアド法でLinear convolution x ** hする。
/// </summary>
/// <param name="h">コンボリューションカーネル。左右反転される。</param>
/// <param name="x">入力数列。</param>
/// <param name="fragmentSz">個々のFFTに入力するxの断片サイズ。</param>
public WWComplex[] ConvolutionContinuousFft(WWComplex[] h, WWComplex[] x, int fragmentSz) {
System.Diagnostics.Debug.Assert(2 <= fragmentSz);
if (x.Length < h.Length) {
// swap x and h
var tmp = h;
h = x;
x = tmp;
}
// h.Len <= x.Len
int fullConvLen = h.Length + x.Length - 1;
var r = new WWComplex[fullConvLen];
for (int i = 0; i < r.Length; ++i) {
r[i] = WWComplex.Zero();
}
// hをFFTしてHを得る。
int fragConvLen = h.Length + fragmentSz - 1;
int fftSize = Functions.NextPowerOf2(fragConvLen);
var h2 = new WWComplex[fftSize];
Array.Copy(h, 0, h2, 0, h.Length);
for (int i = h.Length; i < h2.Length; ++i) {
h2[i] = WWComplex.Zero();
}
var fft = new WWRadix2Fft(fftSize);
var H = fft.ForwardFft(h2);
for (int offs = 0; offs < x.Length; offs += fragmentSz) {
// xFをFFTしてXを得る。
var xF = WWComplex.ZeroArray(fftSize);
for (int i=0; i<fragmentSz; ++i) {
if (i + offs < x.Length) {
xF[i] = x[offs + i];
} else {
break;
}
}
var X = fft.ForwardFft(xF);
var Y = WWComplex.Mul(H, X);
var y = fft.InverseFft(Y);
// オーバーラップアド法。FFT結果を足し合わせる。
for (int i = 0; i <fragConvLen; ++i) {
r[offs + i] = WWComplex.Add(r[offs + i], y[i]);
}
}
return r;
}
/// <summary>
/// Short-time Fourier Transform for frequency domain DSP.
/// time domain data → freq domain data.
/// </summary>
/// <param name="processBlockSize">FFT size</param>
public WWTimeDependentForwardFourierTransform(int processBlockSize, WindowType windowType)
{
if (!Functions.IsPowerOfTwo(processBlockSize) || processBlockSize < 4)
{
throw new ArgumentException("processBlockSize should be power of two and 4 or larger int");
}
mProcessBlockSize = processBlockSize;
mOutputCounter = 0;
PrepareWindow(processBlockSize + 1, windowType);
mFFT = new WWRadix2Fft(processBlockSize);
}
public WWTimeDependentInverseFourierTransform(int processBlockSize)
{
if (!Functions.IsPowerOfTwo(processBlockSize) || processBlockSize < 4)
{
throw new ArgumentException("processBlockSize should be power of two and 4 or larger int");
}
mProcessBlockSize = processBlockSize;
mProcessCounter = 0;
mProcessedSamples = 0;
mFFT = new WWRadix2Fft(processBlockSize);
mOverlapBuff = new double[WantSamples];
}
