private static void ComputeButterworthHighpassCoefficients(
ref IIR2DirectIRec Coeff,
double Cutoff,
double SamplingRate)
{
double C;
double A0;
double HalfSamplingRate;
double HalfSamplingRateMinusEpsilon;
HalfSamplingRate = SamplingRate * 0.5;
HalfSamplingRateMinusEpsilon = HalfSamplingRate - FILTER_FREQ_EPSILON;
if (Cutoff < FILTER_FREQ_EPSILON)
{
Cutoff = FILTER_FREQ_EPSILON;
}
if (Cutoff > HalfSamplingRateMinusEpsilon)
{
Cutoff = HalfSamplingRateMinusEpsilon;
}
C = Math.Tan(Math.PI * Cutoff / SamplingRate);
A0 = 1 / (1 + SQRT2 * C + C * C);
Coeff.A0 = (float)A0;
Coeff.A1 = (float)(-2 * A0);
Coeff.A2 = (float)A0;
Coeff.B1 = (float)(2 * (C * C - 1) * A0);
Coeff.B2 = (float)((1 - SQRT2 * C + C * C) * A0);
}
public static void ComputeButterworthBandpassCoefficients(
ref IIR2DirectIRec Coeff,
double Cutoff,
double Bandwidth,
double SamplingRate)
{
double C;
double D;
double A0;
double HalfSamplingRate;
double OneOverSamplingRateTimesPi;
double HalfSamplingRateMinusEpsilon;
double BandwidthTan;
double CutoffCos;
HalfSamplingRate = SamplingRate * 0.5;
OneOverSamplingRateTimesPi = Math.PI / SamplingRate;
HalfSamplingRateMinusEpsilon = HalfSamplingRate - FILTER_FREQ_EPSILON;
if (Bandwidth < FILTER_FREQ_EPSILON)
{
Bandwidth = FILTER_FREQ_EPSILON;
}
if (Bandwidth > HalfSamplingRateMinusEpsilon)
{
Bandwidth = HalfSamplingRateMinusEpsilon;
}
if (Cutoff < FILTER_FREQ_EPSILON)
{
Cutoff = FILTER_FREQ_EPSILON;
}
if (Cutoff > HalfSamplingRateMinusEpsilon)
{
Cutoff = HalfSamplingRateMinusEpsilon;
}
BandwidthTan = Bandwidth * OneOverSamplingRateTimesPi;
CutoffCos = Cutoff * OneOverSamplingRateTimesPi;
BandwidthTan = Math.Tan(BandwidthTan);
CutoffCos = Math.Cos(CutoffCos + CutoffCos); /* 2 * CutoffCos */
C = 1 / BandwidthTan;
D = CutoffCos + CutoffCos; /* 2 * CutoffCos */
A0 = 1 / (1 + C);
Coeff.A0 = (float)A0;
Coeff.A1 = 0;
Coeff.A2 = (float)(-A0);
Coeff.B1 = (float)(-C * D * A0);
Coeff.B2 = (float)((C - 1) * A0);
}
private static void ComputeParametricEqualizer2Coefficients(
ref IIR2DirectIRec Coeff,
double Cutoff,
double Bandwidth,
double Gain,
double SamplingRate)
{
double Gamma;
double SqrtK;
double HalfSamplingRate;
double OneOverHalfSamplingRateTimesPi;
double OneOverBigGammaSqrtKThing;
double CutoffCos;
HalfSamplingRate = SamplingRate * 0.5;
OneOverHalfSamplingRateTimesPi = Math.PI / HalfSamplingRate;
if (Bandwidth < FILTER_FREQ_EPSILON)
{
Bandwidth = FILTER_FREQ_EPSILON;
}
if (Bandwidth > HalfSamplingRate - FILTER_FREQ_EPSILON)
{
Bandwidth = HalfSamplingRate - FILTER_FREQ_EPSILON;
}
if (Cutoff < FILTER_FREQ_EPSILON)
{
Cutoff = FILTER_FREQ_EPSILON;
}
if (Cutoff > HalfSamplingRate - FILTER_FREQ_EPSILON)
{
Cutoff = HalfSamplingRate - FILTER_FREQ_EPSILON;
}
Cutoff = Cutoff * OneOverHalfSamplingRateTimesPi;
Bandwidth = Bandwidth * OneOverHalfSamplingRateTimesPi * 0.5;
Gamma = Math.Tan(Bandwidth);
SqrtK = Math.Sqrt(Gain);
CutoffCos = Math.Cos(Cutoff);
OneOverBigGammaSqrtKThing = 1 / (1 + Gamma / SqrtK);
Coeff.A1 = (float)((-2 * CutoffCos) * OneOverBigGammaSqrtKThing);
Coeff.A0 = (float)((1 + Gamma * SqrtK) * OneOverBigGammaSqrtKThing);
Coeff.A2 = (float)((1 - Gamma * SqrtK) * OneOverBigGammaSqrtKThing);
Coeff.B1 = Coeff.A1;
Coeff.B2 = (float)((1 - Gamma / SqrtK) * OneOverBigGammaSqrtKThing);
}
private static void ComputeButterworthBandrejectCoefficients(
ref IIR2DirectIRec Coeff,
double Cutoff,
double Bandwidth,
double SamplingRate)
{
double C;
double D;
double A0;
double HalfSamplingRate;
double OneOverSamplingRate;
double HalfSamplingRateMinusEpsilon;
HalfSamplingRate = SamplingRate * 0.5;
OneOverSamplingRate = 1.0 / SamplingRate;
HalfSamplingRateMinusEpsilon = HalfSamplingRate - FILTER_FREQ_EPSILON;
if (Bandwidth < FILTER_FREQ_EPSILON)
{
Bandwidth = FILTER_FREQ_EPSILON;
}
if (Bandwidth > HalfSamplingRateMinusEpsilon)
{
Bandwidth = HalfSamplingRateMinusEpsilon;
}
if (Cutoff < FILTER_FREQ_EPSILON)
{
Cutoff = FILTER_FREQ_EPSILON;
}
if (Cutoff > HalfSamplingRateMinusEpsilon)
{
Cutoff = HalfSamplingRateMinusEpsilon;
}
C = Math.Tan(Math.PI * Bandwidth * OneOverSamplingRate);
D = 2 * Math.Cos(TWOPI * Cutoff * OneOverSamplingRate);
A0 = 1 / (1 + C);
Coeff.A0 = (float)A0;
Coeff.A1 = (float)(-D * A0);
Coeff.A2 = (float)A0;
Coeff.B1 = (float)(-D * A0);
Coeff.B2 = (float)((1 - C) * A0);
}
private static void ComputeHighShelfEqualizerCoefficients(
ref IIR2DirectIRec Coeff,
double Cutoff,
double Slope,
double Gain,
double SamplingRate)
{
double HalfSamplingRate;
double A;
double Omega;
double CS;
double SN;
double Beta;
double OneOverB0;
HalfSamplingRate = SamplingRate * 0.5;
if (Cutoff < FILTER_FREQ_EPSILON)
{
Cutoff = FILTER_FREQ_EPSILON;
}
if (Cutoff > HalfSamplingRate - FILTER_FREQ_EPSILON)
{
Cutoff = HalfSamplingRate - FILTER_FREQ_EPSILON;
}
A = Math.Sqrt(Gain);
Omega = TWOPI * Cutoff / SamplingRate;
CS = Math.Cos(Omega);
SN = Math.Sin(Omega);
Beta = Math.Sqrt((A * A + 1) / Slope - ((A - 1) * (A - 1)));
OneOverB0 = 1 / ((A + 1) - (A - 1) * CS + Beta * SN);
Coeff.A0 = (float)(OneOverB0 * A * ((A + 1) + (A - 1) * CS + Beta * SN));
Coeff.A1 = (float)(OneOverB0 * -2 * A * ((A - 1) + (A + 1) * CS));
Coeff.A2 = (float)(OneOverB0 * A * ((A + 1) + (A - 1) * CS - Beta * SN));
Coeff.B1 = (float)(OneOverB0 * 2 * ((A - 1) - (A + 1) * CS));
Coeff.B2 = (float)(OneOverB0 * ((A + 1) - (A - 1) * CS - Beta * SN));
}
