/* apply filter to an array of values, adding result to output array */
public void Apply(
float[] XinVector,
int XinVectorOffset,
float[] YoutVector,
int YoutVectorOffset,
int VectorLength,
float OutputScaling,
SynthParamRec SynthParams)
{
SecondOrderZeroRec Filter = this;
float Xm1 = Filter.Xm1;
float Xm2 = Filter.Xm2;
float A0 = Filter.A0;
float A1 = Filter.A1;
float A2 = Filter.A2;
for (int i = 0; i < VectorLength; i += 1)
{
float Xin = XinVector[i + XinVectorOffset];
float OrigYOut = YoutVector[i + YoutVectorOffset];
float Y = A0 * Xin + A1 * Xm1 + A2 * Xm2;
Xm2 = Xm1;
Xm1 = Xin;
YoutVector[i + YoutVectorOffset] = OrigYOut + Y * OutputScaling;
}
Filter.Xm1 = Xm1;
Filter.Xm2 = Xm2;
}
public static void SetSecondOrderZeroCoefficients(
SecondOrderZeroRec Filter,
double Cutoff,
double Bandwidth,
FilterScalings Scaling,
double SamplingRate)
{
double C2;
double C1;
double D;
double HalfSamplingRateMinusEpsilon;
double OneOverD;
double OneOverSamplingRate;
HalfSamplingRateMinusEpsilon = SamplingRate * 0.5 - FILTER_FREQ_EPSILON;
OneOverSamplingRate = 1.0 / SamplingRate;
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;
}
C2 = Math.Exp(NEGTWOPI * Bandwidth * OneOverSamplingRate);
C1 = (-4 * C2 / (1 + C2)) * Math.Cos(TWOPI * Cutoff * OneOverSamplingRate);
switch (Scaling)
{
default:
Debug.Assert(false);
throw new ArgumentException();
case FilterScalings.eFilterDefaultScaling:
D = 1;
break;
case FilterScalings.eFilterZeroGain1:
D = 1 + C1 + C2;
break;
}
OneOverD = 1 / D;
Filter.A0 = (float)OneOverD;
Filter.A1 = (float)(C1 * OneOverD);
Filter.A2 = (float)(C2 * OneOverD);
}
