/* 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)
{
SecondOrderResonRec Filter = this;
float Ym1 = Filter.Ym1;
float Ym2 = Filter.Ym2;
float A0 = Filter.A0;
float B1 = Filter.B1;
float B2 = Filter.B2;
for (int i = 0; i < VectorLength; i += 1)
{
float Xin = XinVector[i + XinVectorOffset];
float OrigYOut = YoutVector[i + YoutVectorOffset];
float Y = A0 * Xin - B1 * Ym1 - B2 * Ym2;
Ym2 = Ym1;
Ym1 = Y;
YoutVector[i + YoutVectorOffset] = OrigYOut + Y * OutputScaling;
}
Filter.Ym1 = Ym1;
Filter.Ym2 = Ym2;
}
public static void SetSecondOrderResonCoefficients(
SecondOrderResonRec Filter,
double Cutoff,
double Bandwidth,
FilterScalings Scaling,
double SamplingRate)
{
double B1;
double B2;
double OneOverSamplingRate;
double HalfSamplingRateMinusEpsilon;
OneOverSamplingRate = 1 / SamplingRate;
HalfSamplingRateMinusEpsilon = SamplingRate * 0.5 - 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;
}
B2 = Math.Exp(NEGTWOPI * Bandwidth * OneOverSamplingRate);
Filter.B2 = (float)B2;
B1 = ((-4 * B2) / (1 + B2)) * Math.Cos(TWOPI * Cutoff * OneOverSamplingRate);
Filter.B1 = (float)B1;
switch (Scaling)
{
default:
Debug.Assert(false);
throw new ArgumentException();
case FilterScalings.eFilterDefaultScaling:
Filter.A0 = 1;
break;
case FilterScalings.eFilterResonMidbandGain1:
Filter.A0 = (float)((1 - B2) * Math.Sqrt(1 - B1 * B1 / (4 * B2)));
break;
case FilterScalings.eFilterResonNoiseGain1:
double X = 1 + B2;
double Y = 1 - B2;
Filter.A0 = (float)(Math.Sqrt((X * X - B1 * B1) * Y / X));
break;
}
}
