private void SetupCoeffs()
{
var window = WWWindowFunc.BlackmanWindow(WindowLength);
// ループ処理を簡単にするため最初と最後に0を置く。
mCoeffs = new double[1 + WindowLength + 1];
int center = WindowLength / 2;
for (int i = 0; i < WindowLength / 2 + 1; ++i)
{
int numerator = i;
int denominator = Factor;
int numeratorReminder = numerator % (denominator * 2);
if (numerator == 0)
{
mCoeffs[1 + center + i] = 1.0f;
}
else if (numerator % denominator == 0)
{
// sinc(180 deg) == 0, sinc(360 deg) == 0, ...
mCoeffs[1 + center + i] = 0.0f;
}
else
{
mCoeffs[1 + center + i] = Math.Sin(Math.PI * numeratorReminder / denominator)
/ (Math.PI * numerator / denominator)
* window[center + i];
}
mCoeffs[1 + center - i] = mCoeffs[1 + center + i];
}
}
public OverlappedFft(int fftLength)
{
mFftLength = fftLength;
mFft = new WWRadix2Fft(mFftLength);
mOverlapInputSamples = new double[mFftLength / 2];
mWindow = WWWindowFunc.BlackmanWindow(mFftLength / 2 - 1);
mLastOutputSamplesTail = new double[mFftLength / mSpliceDenominator];
mFirstTime = true;
}
private void DesignFilter()
{
mFilterCoeffs = new double[FilterLength];
var sine90Table = new double[] { 0.0, 1.0, 0.0, -1.0 };
for (int i = 0; i < FILTER_DELAY; ++i)
{
if (i != 0 && 0 == (i & 1))
{
// coefficient is 0
continue;
}
double theta = Math.PI * (i * 90.0) / 180.0f;
double v = 1.0;
if (Double.Epsilon < Math.Abs(theta))
{
v = sine90Table[i & 3] / theta;
}
mFilterCoeffs[FILTER_DELAY - 1 - i] = v;
mFilterCoeffs[FILTER_DELAY - 1 + i] = v;
}
// Kaiser窓(α==9)をかける
var w = WWWindowFunc.KaiserWindow(FilterLength, 9.0);
for (int i = 0; i < FilterLength; ++i)
{
mFilterCoeffs[i] *= w[i];
}
// 0.5倍する
for (int i = 0; i < FilterLength; ++i)
{
mFilterCoeffs[i] *= 0.5;
}
}
private void DesignCutoffFilter()
{
var fromF = new WWComplex[FILTER_LENP1];
// バターワースフィルター
// 1次 = 6dB/oct
// 2次 = 12dB/oct
double orderX2 = 2.0 * (FilterSlopeDbOct / 6.0);
double cutoffRatio = CutoffFrequency / (SampleRate / 2);
// フィルタのF特
fromF[0].real = 1.0f;
for (int i = 1; i <= FILTER_LENP1 / 2; ++i)
{
double omegaRatio = i * (1.0 / (FILTER_LENP1 / 2));
double v = Math.Sqrt(1.0 / (1.0 + Math.Pow(omegaRatio / cutoffRatio, orderX2)));
if (Math.Abs(v) < Math.Pow(0.5, 24))
{
v = 0.0;
}
fromF[i].real = v;
}
for (int i = 1; i < FILTER_LENP1 / 2; ++i)
{
fromF[FILTER_LENP1 - i].real = fromF[i].real;
}
// IFFTでfromFをfromTに変換
var fromT = new WWComplex[FILTER_LENP1];
{
var fft = new WWRadix2Fft(FILTER_LENP1);
fft.ForwardFft(fromF, fromT);
double compensation = 1.0 / (FILTER_LENP1 * cutoffRatio);
for (int i = 0; i < FILTER_LENP1; ++i)
{
fromT[i].Set(
fromT[i].real * compensation,
fromT[i].imaginary * compensation);
}
}
fromF = null;
// fromTの中心がFILTER_LENGTH/2番に来るようにする。
// delayT[0]のデータはfromF[FILTER_LENGTH/2]だが、非対称になるので入れない
// このフィルタの遅延はFILTER_LENGTH/2サンプルある
var delayT = new WWComplex[FILTER_LENP1];
for (int i = 1; i < FILTER_LENP1 / 2; ++i)
{
delayT[i] = fromT[i + FILTER_LENP1 / 2];
}
for (int i = 0; i < FILTER_LENP1 / 2; ++i)
{
delayT[i + FILTER_LENP1 / 2] = fromT[i];
}
fromT = null;
// Kaiser窓をかける
var w = WWWindowFunc.KaiserWindow(FILTER_LENP1 + 1, 9.0);
for (int i = 0; i < FILTER_LENP1; ++i)
{
delayT[i].Mul(w[i]);
}
var delayTL = new WWComplex[FFT_LEN];
for (int i = 0; i < delayT.Length; ++i)
{
delayTL[i] = delayT[i];
}
delayT = null;
// できたフィルタをFFTする
var delayF = new WWComplex[FFT_LEN];
{
var fft = new WWRadix2Fft(FFT_LEN);
fft.ForwardFft(delayTL, delayF);
for (int i = 0; i < FFT_LEN; ++i)
{
delayF[i].Mul(cutoffRatio);
}
}
delayTL = null;
mFilterFreq = delayF;
}
public override double[] FilterDo(double[] inPcm)
{
System.Diagnostics.Debug.Assert(inPcm.Length == NumOfSamplesNeeded());
var inPcmR = new double[FftLength];
if (mFirst)
{
Array.Copy(inPcm, 0, inPcmR, HalfOverlapLength, inPcm.Length);
}
else
{
System.Diagnostics.Debug.Assert(mOverlapSamples != null);
System.Diagnostics.Debug.Assert(mOverlapSamples.Length == HalfOverlapLength * 2);
Array.Copy(mOverlapSamples, 0, inPcmR, 0, HalfOverlapLength * 2);
mOverlapSamples = null;
Array.Copy(inPcm, 0, inPcmR, HalfOverlapLength * 2, inPcm.Length);
}
var inPcmT = new WWComplex[FftLength];
for (int i = 0; i < inPcmT.Length; ++i)
{
inPcmT[i] = new WWComplex(inPcmR[i], 0);
}
{
// inPcmTの出力されず捨てられる領域に窓関数を掛ける。
// Kaiser窓(α==9)をかける
var w = WWWindowFunc.KaiserWindow(HalfOverlapLength * 2, 9.0);
for (int i = 0; i < HalfOverlapLength; ++i)
{
inPcmT[i].Mul(w[i]);
inPcmT[FftLength - i - 1].Mul(w[i]);
}
}
// inPcmTをFFTしてinPcmFを得る。
WWComplex[] inPcmF;
{
var fft = new WWRadix2Fft(FftLength);
inPcmF = fft.ForwardFft(inPcmT);
}
inPcmT = null;
// inPcmFを0で水増ししたデータoutPcmFを作ってローパスフィルターを通し逆FFTしoutPcmTを得る。
var outPcmF = new WWComplex[UpsampleFftLength];
for (int i = 0; i < outPcmF.Length; ++i)
{
if (i <= FftLength / 2)
{
outPcmF[i].CopyFrom(inPcmF[i]);
}
else if (UpsampleFftLength - FftLength / 2 <= i)
{
int pos = i + FftLength - UpsampleFftLength;
outPcmF[i].CopyFrom(inPcmF[pos]);
}
else
{
// do nothing
}
outPcmF[i].Mul(mFreqFilter[i]);
}
inPcmF = null;
WWComplex[] outPcmT;
{
var fft = new WWRadix2Fft(UpsampleFftLength);
outPcmT = fft.InverseFft(outPcmF, 1.0 / FftLength);
}
outPcmF = null;
// outPcmTの実数成分を戻り値とする。
var outPcm = new double[Factor * (FftLength - HalfOverlapLength * 2)];
for (int i = 0; i < outPcm.Length; ++i)
{
outPcm[i] = outPcmT[i + Factor * HalfOverlapLength].real;
}
outPcmT = null;
// 次回計算に使用するオーバーラップ部分のデータをmOverlapSamplesに保存。
// オーバラップ部分==inPcmRの最後の方
mOverlapSamples = new double[HalfOverlapLength * 2];
Array.Copy(inPcmR, inPcmR.Length - HalfOverlapLength * 2, mOverlapSamples, 0, HalfOverlapLength * 2);
if (mFirst)
{
mFirst = false;
}
return(outPcm);
}
/// <summary>
/// バターワースフィルターのFFT coeffs
/// </summary>
/// <param name="filterSlopeDbOct">1次 = 6(dB/oct), 2次 = 12(dB/oct)</param>
/// <returns></returns>
public static WWComplex[] Design(int sampleRate, double cutoffFrequency, int fftLength, int filterSlopeDbOct)
{
int filterLenP1 = fftLength / 4;
int filterLength = filterLenP1 - 1;
var fromF = new WWComplex[filterLenP1];
double orderX2 = 2.0 * (filterSlopeDbOct / 6.0);
double cutoffRatio = cutoffFrequency / (sampleRate / 2);
// フィルタのF特
fromF[0].real = 1.0f;
for (int i = 1; i <= filterLenP1 / 2; ++i)
{
double omegaRatio = i * (1.0 / (filterLenP1 / 2));
double v = Math.Sqrt(1.0 / (1.0 + Math.Pow(omegaRatio / cutoffRatio, orderX2)));
if (Math.Abs(v) < Math.Pow(0.5, 24))
{
v = 0.0;
}
fromF[i].real = v;
}
for (int i = 1; i < filterLenP1 / 2; ++i)
{
fromF[filterLenP1 - i].real = fromF[i].real;
}
// IFFTでfromFをfromTに変換
WWComplex[] fromT;
{
var fft = new WWRadix2Fft(filterLenP1);
fromT = fft.ForwardFft(fromF);
double compensation = 1.0 / (filterLenP1 * cutoffRatio);
for (int i = 0; i < filterLenP1; ++i)
{
fromT[i].Set(
fromT[i].real * compensation,
fromT[i].imaginary * compensation);
}
}
fromF = null;
// fromTの中心がFILTER_LENGTH/2番に来るようにする。
// delayT[0]のデータはfromF[FILTER_LENGTH/2]だが、非対称になるので入れない
// このフィルタの遅延はFILTER_LENGTH/2サンプルある
var delayT = new WWComplex[filterLenP1];
for (int i = 1; i < filterLenP1 / 2; ++i)
{
delayT[i] = fromT[i + filterLenP1 / 2];
}
for (int i = 0; i < filterLenP1 / 2; ++i)
{
delayT[i + filterLenP1 / 2] = fromT[i];
}
fromT = null;
// Kaiser窓をかける
var w = WWWindowFunc.KaiserWindow(filterLenP1 + 1, 9.0);
for (int i = 0; i < filterLenP1; ++i)
{
delayT[i].Mul(w[i]);
}
var delayTL = new WWComplex[fftLength];
for (int i = 0; i < delayT.Length; ++i)
{
delayTL[i] = delayT[i];
}
delayT = null;
// できたフィルタをFFTする
WWComplex[] delayF;
{
var fft = new WWRadix2Fft(fftLength);
delayF = fft.ForwardFft(delayTL);
for (int i = 0; i < fftLength; ++i)
{
delayF[i].Mul(cutoffRatio);
}
}
delayTL = null;
return(delayF);
}
