/* 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)
{
ParametricEqualizerRec Filter = this;
float State1 = Filter.State1;
float State0 = Filter.State0;
float A = Filter.A;
float B = Filter.B;
float K = Filter.K;
float OneMinusK = 1 - K;
float OnePlusK = 1 + K;
for (int i = 0; i < VectorLength; i += 1)
{
float Xin = XinVector[i + XinVectorOffset];
float OrigYOut = YoutVector[i + YoutVectorOffset];
float Allpass = A * (Xin - A * State1) + State1;
float Outval = .5f * (OnePlusK * Xin + OneMinusK * Allpass);
float Temp = Xin - A * State1 - B * State0;
State1 = B * Temp + State0;
State0 = Temp;
YoutVector[i + YoutVectorOffset] = OrigYOut + Outval * OutputScaling;
}
Filter.State1 = State1;
Filter.State0 = State0;
}
public static void SetParametricEqualizerCoefficients(
ParametricEqualizerRec Filter,
double Cutoff,
double Bandwidth,
double Gain,
double SamplingRate)
{
double X;
double OneOverSamplingRate;
if ((Cutoff == Filter.OldCutoff) && (Bandwidth == Filter.OldBandwidth) && (Gain == Filter.OldGain))
{
return;
}
Filter.OldCutoff = Cutoff;
Filter.OldBandwidth = Bandwidth;
Filter.OldGain = Gain;
OneOverSamplingRate = 1.0 / SamplingRate;
if (Bandwidth < FILTER_FREQ_EPSILON)
{
Bandwidth = FILTER_FREQ_EPSILON;
}
if (Bandwidth > SamplingRate * 0.25 - FILTER_FREQ_EPSILON)
{
Bandwidth = SamplingRate * 0.25 - FILTER_FREQ_EPSILON;
}
if (Cutoff < FILTER_FREQ_EPSILON)
{
Cutoff = FILTER_FREQ_EPSILON;
}
if (Cutoff > SamplingRate * 0.5 - FILTER_FREQ_EPSILON)
{
Cutoff = SamplingRate * 0.5 - FILTER_FREQ_EPSILON;
}
X = Math.Tan(TWOPI * Bandwidth * OneOverSamplingRate);
Filter.A = (float)((1 - X) / (1 + X));
Filter.B = (float)(-Math.Cos(TWOPI * Cutoff * OneOverSamplingRate));
Filter.K = (float)Gain;
}
