/// <summary>
/// 線形位相バンドパスフィルタの係数を計算する。
/// 右側半分のみを計算。
/// </summary>
/// <param name="type">フィルタタイプ</param>
/// <param name="n">タップ数＝2n+1</param>
/// <param name="w">遮断周波数(BPF の場合は遮断帯域幅、HPF の場合は π-遮断周波数)</param>
/// <param name="w0">(BPF のみ) 中心周波数</param>
/// <param name="window">窓関数</param>
/// <returns>係数の右側半分を計算したもの</returns>
public static void CalcLinearBPFCoefficient(FirFilterType type, double[] coef, double w, double w0, WindowFunction window)
{
int n = coef.Length;
double sum;
sum = coef[0] = window(0) * w;
for(int i=1; i<n; ++i)
{
double tmp = window(i) * Math.Sin(w * i) / i;
sum += tmp * 2;
if(type == FirFilterType.LPF)
{
coef[i] = tmp;
}
else if(type == FirFilterType.HPF)
{
if(i%2 != 0)
coef[i] = -tmp;
else
coef[i] = tmp;
}
else
{
coef[i] = 2 * Math.Cos(w0 * i) * tmp;
}
}
for(int i=0; i<n; ++i)
{
coef[i] /= sum;
}
}//GetLinearBPFCoefficient
public static string ToFriendlyString(this FirFilterType type)
{
switch (type)
{
case FirFilterType.LowPass:
return("Низкочастотный фильтр");
case FirFilterType.HighPass:
return("Высокочастотный фильтр");
default:
throw new Exception();
break;
}
}
public static IFirFilter CalcLinearBPFCoefficient(FirFilterType type, double w, double w0, int taps, WindowType window)
{
double[] coef;
if (taps % 2 == 1)
{
coef = new double[(taps + 1) / 2];
CalcOddLinearBPFCoefficient(type, coef, w, w0, GetWindow(window, taps));
return(new OddLinearFir(coef));
}
else
{
coef = new double[taps / 2];
CalcEvenLinearBPFCoefficient(type, coef, w, w0, GetWindow(window, taps));
return(new EvenLinearFir(coef));
}
}
public static IFirFilter CalcLinearBPFCoefficient(FirFilterType type, double w, double w0, int taps, WindowType window)
{
double[] coef;
if(taps % 2 == 1)
{
coef = new double[(taps + 1) / 2];
CalcOddLinearBPFCoefficient(type, coef, w, w0, GetWindow(window, taps));
return new OddLinearFir(coef);
}
else
{
coef = new double[taps / 2];
CalcEvenLinearBPFCoefficient(type, coef, w, w0, GetWindow(window, taps));
return new EvenLinearFir(coef);
}
}
} //GetOddLinearBPFCoefficient
/// <summary>
/// 線形位相バンドパスフィルタ(奇数タップ)の係数を計算する。
/// 右側半分のみを計算。
/// </summary>
/// <param name="type">フィルタタイプ</param>
/// <param name="coef">係数の格納先</param>
/// <param name="w">遮断周波数(BPF の場合は遮断帯域幅、HPF の場合は π-遮断周波数)</param>
/// <param name="w0">(BPF のみ) 中心周波数</param>
/// <param name="window">窓関数</param>
public static void CalcEvenLinearBPFCoefficient(FirFilterType type, double[] coef, double w, double w0, WindowFunction window)
{
int n = coef.Length - 1;
double sum;
sum = 0;
for (int i = 0; i <= n; ++i)
{
double x = i + 0.5;
double tmp = window(x) * Math.Sin(w * x) / x;
sum += tmp * 2;
if (type == FirFilterType.LPF)
{
coef[n - i] = tmp;
}
else if (type == FirFilterType.HPF)
{
if (i % 2 != 0)
{
coef[n - i] = -tmp;
}
else
{
coef[n - i] = tmp;
}
}
else
{
coef[n - i] = 2 * Math.Cos(w0 * x) * tmp;
}
}
for (int i = 0; i < n; ++i)
{
coef[i] /= sum;
}
} //GetEvenLinearBPFCoefficient
/// <summary>
/// 線形位相バンドパスフィルタ(奇数タップ)の係数を計算する。
/// 右側半分のみを計算。
/// </summary>
/// <param name="type">フィルタタイプ</param>
/// <param name="coef">係数の格納先</param>
/// <param name="w">遮断周波数(BPF の場合は遮断帯域幅、HPF の場合は π-遮断周波数)</param>
/// <param name="w0">(BPF のみ) 中心周波数</param>
/// <param name="window">窓関数</param>
public static void CalcOddLinearBPFCoefficient(FirFilterType type, double[] coef, double w, double w0, WindowFunction window)
{
int n = coef.Length - 1;
double sum;
sum = coef[n] = window(0) * w;
for (int i = 1; i <= n; ++i)
{
double tmp = window(i) * Math.Sin(w * i) / i;
sum += tmp * 2;
if (type == FirFilterType.LPF)
{
coef[n - i] = tmp;
}
else if (type == FirFilterType.HPF)
{
if (i % 2 != 0)
{
coef[n - i] = -tmp;
}
else
{
coef[n - i] = tmp;
}
}
else
{
coef[n - i] = 2 * Math.Cos(w0 * i) * tmp;
}
}
for (int i = 0; i <= n; ++i)
{
coef[i] /= sum;
}
} //GetOddLinearBPFCoefficient
}//GetOddLinearBPFCoefficient
/// <summary>
/// 線形位相バンドパスフィルタ(奇数タップ)の係数を計算する。
/// 右側半分のみを計算。
/// </summary>
/// <param name="type">フィルタタイプ</param>
/// <param name="coef">係数の格納先</param>
/// <param name="w">遮断周波数(BPF の場合は遮断帯域幅、HPF の場合は π-遮断周波数)</param>
/// <param name="w0">(BPF のみ) 中心周波数</param>
/// <param name="window">窓関数</param>
public static void CalcEvenLinearBPFCoefficient(FirFilterType type, double[] coef, double w, double w0, WindowFunction window)
{
int n = coef.Length - 1;
double sum;
sum = 0;
for(int i=0; i<=n; ++i)
{
double x = i + 0.5;
double tmp = window(x) * Math.Sin(w * x) / x;
sum += tmp * 2;
if(type == FirFilterType.LPF)
{
coef[n - i] = tmp;
}
else if(type == FirFilterType.HPF)
{
if(i%2 != 0)
coef[n - i] = -tmp;
else
coef[n - i] = tmp;
}
else
{
coef[n - i] = 2 * Math.Cos(w0 * x) * tmp;
}
}
for(int i=0; i<n; ++i)
{
coef[i] /= sum;
}
}//GetEvenLinearBPFCoefficient
public static double[] ImpulseCharacteristic(double hz, int n, double threshold, FirFilterType impulseCharacteristicType = FirFilterType.LowPass, FirWindowType windowType = FirWindowType.Rectangle)
{
double[] h;
double[] w = WindowCoef(windowType, n);
double fc = threshold / (hz);
switch (impulseCharacteristicType)
{
case FirFilterType.LowPass:
h = BaseImpulseCharacteristic(threshold, hz, n);
break;
case FirFilterType.HighPass:
h = BaseImpulseCharacteristic(threshold, hz, n).Select(x => (-x)).ToArray();
h[n / 2] = 1 - 2 * fc;
break;
default:
throw new Exception();
}
double[] result = new double[n];
for (int i = 0; i < n; i++)
{
result[i] = h[i] * w[i];
}
return(result);
}
public static double[] FirFilter(double[] data, double hz, int n, double threshold0, double threshold1, FirFilterType type = FirFilterType.LowPass, FirWindowType windowType = FirWindowType.Rectangle)
{
double[] h = ImpulseCharacteristic(hz, n, threshold0, threshold1, type, windowType);
return(BaseFirFilter(data, h));
}
public static double[] ImpulseCharacteristic(double hz, int n, double threshold0, double threshold1, FirFilterType impulseCharacteristicType = FirFilterType.LowPass, FirWindowType windowType = FirWindowType.Rectangle)
{
double[] h0, h1, h;
double[] w = WindowCoef(windowType, n);
double fc0 = threshold0 / (hz);
double fc1 = threshold1 / (hz);
switch (impulseCharacteristicType)
{
case FirFilterType.BandPass:
h = new double[n];
h0 = BaseImpulseCharacteristic(threshold0, hz, n);
h1 = BaseImpulseCharacteristic(threshold1, hz, n);
for (int i = 0; i < n; i++)
{
h[i] = h1[i] - h0[i];
h[n / 2] = 2 * (fc1 - fc0);
}
break;
case FirFilterType.NotchPass:
h = new double[n];
h0 = BaseImpulseCharacteristic(threshold0, hz, n);
h1 = BaseImpulseCharacteristic(threshold1, hz, n);
for (int i = 0; i < n; i++)
{
h[i] = h0[i] - h1[i];
h[n / 2] = 1 - 2 * (fc1 - fc0);
}
break;
default:
throw new Exception();
}
double[] result = new double[n];
for (int i = 0; i < n; i++)
{
result[i] = h[i] * w[i];
}
return(result);
}
