public void Init(IirFilterType filterType, double frequency, double sampleRate, int qualityFactor)
{
var w0 = 2.0 * Math.PI * frequency / sampleRate;
var alpha = Math.Sin(w0) / (2.0 * qualityFactor);
switch (filterType)
{
case IirFilterType.LowPass:
_b0 = (float)((1.0 - Math.Cos(w0)) / 2.0);
_b1 = (float)(1.0 - Math.Cos(w0));
_b2 = (float)((1.0 - Math.Cos(w0)) / 2.0);
_a0 = (float)(1.0 + alpha);
_a1 = (float)(-2.0 * Math.Cos(w0));
_a2 = (float)(1.0 - alpha);
break;
case IirFilterType.HighPass:
_b0 = (float)((1.0 + Math.Cos(w0)) / 2.0);
_b1 = (float)(-(1.0 + Math.Cos(w0)));
_b2 = (float)((1.0 + Math.Cos(w0)) / 2.0);
_a0 = (float)(1.0 + alpha);
_a1 = (float)(-2.0 * Math.Cos(w0));
_a2 = (float)(1.0 - alpha);
break;
//case IirFilterType.BandPass:
default:
_b0 = (float)(alpha);
_b1 = 0.0f;
_b2 = (float)(-alpha);
_a0 = (float)(1.0 + alpha);
_a1 = (float)(-2.0 * Math.Cos(w0));
_a2 = (float)(1.0 - alpha);
break;
case IirFilterType.Notch:
_b0 = 1.0f;
_b1 = (float)(-2.0 * Math.Cos(w0));
_b2 = 1.0f;
_a0 = (float)(1.0 + alpha);
_a1 = (float)(-2.0 * Math.Cos(w0));
_a2 = (float)(1.0 - alpha);
break;
}
_b0 /= _a0;
_b1 /= _a0;
_b2 /= _a0;
_a1 /= _a0;
_a2 /= _a0;
_x1 = 0;
_x2 = 0;
_y1 = 0;
_y2 = 0;
}
public void Init(IirFilterType filterType, double frequency, double sampleRate, int qualityFactor)
{
var w0 = 2.0 * Math.PI * frequency / sampleRate;
var alpha = Math.Sin(w0) / (2.0 * qualityFactor);
switch (filterType)
{
case IirFilterType.LowPass:
_b0 = (float) ((1.0 - Math.Cos(w0)) / 2.0);
_b1 = (float) ( 1.0 - Math.Cos(w0));
_b2 = (float) ((1.0 - Math.Cos(w0)) / 2.0);
_a0 = (float) ( 1.0 + alpha);
_a1 = (float) (-2.0 * Math.Cos(w0));
_a2 = (float) ( 1.0 - alpha);
break;
case IirFilterType.HighPass:
_b0 = (float) ( (1.0 + Math.Cos(w0)) / 2.0);
_b1 = (float) (-(1.0 + Math.Cos(w0)));
_b2 = (float) ( (1.0 + Math.Cos(w0)) / 2.0);
_a0 = (float) ( 1.0 + alpha);
_a1 = (float) ( -2.0 * Math.Cos(w0));
_a2 = (float) ( 1.0 - alpha);
break;
//case IirFilterType.BandPass:
default:
_b0 = (float) (alpha);
_b1 = 0.0f;
_b2 = (float) (-alpha);
_a0 = (float) ( 1.0 + alpha);
_a1 = (float) (-2.0 * Math.Cos(w0));
_a2 = (float) ( 1.0 - alpha);
break;
case IirFilterType.Notch:
_b0 = 1.0f;
_b1 = (float) (-2.0 * Math.Cos(w0));
_b2 = 1.0f;
_a0 = (float) ( 1.0 + alpha);
_a1 = (float) (-2.0 * Math.Cos(w0));
_a2 = (float) ( 1.0 - alpha);
break;
}
_b0 /= _a0;
_b1 /= _a0;
_b2 /= _a0;
_a1 /= _a0;
_a2 /= _a0;
_x1 = 0;
_x2 = 0;
_y1 = 0;
_y2 = 0;
}
public void Init(IirFilterType filterType, float frequency, float sampleRate, int qualityFactor)
{
var w0 = 2.0f * MathF.PI * frequency / sampleRate;
var alpha = MathF.Sin(w0) / (2.0f * qualityFactor);
switch (filterType)
{
case IirFilterType.LowPass:
_b0 = (1.0f - MathF.Cos(w0)) / 2.0f;
_b1 = 1.0f - MathF.Cos(w0);
_b2 = (1.0f - MathF.Cos(w0)) / 2.0f;
_a0 = 1.0f + alpha;
_a1 = -2.0f * MathF.Cos(w0);
_a2 = 1.0f - alpha;
break;
case IirFilterType.HighPass:
_b0 = (1.0f + MathF.Cos(w0)) / 2.0f;
_b1 = -(1.0f + MathF.Cos(w0));
_b2 = (1.0f + MathF.Cos(w0)) / 2.0f;
_a0 = 1.0f + alpha;
_a1 = -2.0f * MathF.Cos(w0);
_a2 = 1.0f - alpha;
break;
//case IirFilterType.BandPass:
default:
_b0 = alpha;
_b1 = 0.0f;
_b2 = -alpha;
_a0 = 1.0f + alpha;
_a1 = -2.0f * MathF.Cos(w0);
_a2 = 1.0f - alpha;
break;
case IirFilterType.Notch:
_b0 = 1.0f;
_b1 = -2.0f * MathF.Cos(w0);
_b2 = 1.0f;
_a0 = 1.0f + alpha;
_a1 = -2.0f * MathF.Cos(w0);
_a2 = 1.0f - alpha;
break;
}
_b0 /= _a0;
_b1 /= _a0;
_b2 /= _a0;
_a1 /= _a0;
_a2 /= _a0;
_x1 = 0;
_x2 = 0;
_y1 = 0;
_y2 = 0;
}
public void Init(IirFilterType filterType, double frequency, double sampleRate, int qualityFactor)
{
double num = 6.2831853071795862 * frequency / sampleRate;
double num2 = Math.Sin(num) / (2.0 * (double)qualityFactor);
switch (filterType)
{
case IirFilterType.LowPass:
this._b0 = (float)((1.0 - Math.Cos(num)) / 2.0);
this._b1 = (float)(1.0 - Math.Cos(num));
this._b2 = (float)((1.0 - Math.Cos(num)) / 2.0);
this._a0 = (float)(1.0 + num2);
this._a1 = (float)(-2.0 * Math.Cos(num));
this._a2 = (float)(1.0 - num2);
break;
case IirFilterType.HighPass:
this._b0 = (float)((1.0 + Math.Cos(num)) / 2.0);
this._b1 = (float)(0.0 - (1.0 + Math.Cos(num)));
this._b2 = (float)((1.0 + Math.Cos(num)) / 2.0);
this._a0 = (float)(1.0 + num2);
this._a1 = (float)(-2.0 * Math.Cos(num));
this._a2 = (float)(1.0 - num2);
break;
default:
this._b0 = (float)num2;
this._b1 = 0f;
this._b2 = (float)(0.0 - num2);
this._a0 = (float)(1.0 + num2);
this._a1 = (float)(-2.0 * Math.Cos(num));
this._a2 = (float)(1.0 - num2);
break;
case IirFilterType.Notch:
this._b0 = 1f;
this._b1 = (float)(-2.0 * Math.Cos(num));
this._b2 = 1f;
this._a0 = (float)(1.0 + num2);
this._a1 = (float)(-2.0 * Math.Cos(num));
this._a2 = (float)(1.0 - num2);
break;
}
this._b0 /= this._a0;
this._b1 /= this._a0;
this._b2 /= this._a0;
this._a1 /= this._a0;
this._a2 /= this._a0;
this._x1 = 0f;
this._x2 = 0f;
this._y1 = 0f;
this._y2 = 0f;
}
public void Init(IirFilterType filterType, double frequency, double sampleRate, double qualityFactor)
{
double num1 = 2.0 * Math.PI * frequency / sampleRate;
double num2 = Math.Sin(num1) / (2.0 * qualityFactor);
switch (filterType)
{
case IirFilterType.LowPass:
this._b0 = (float) ((1.0 - Math.Cos(num1)) / 2.0);
this._b1 = (float) (1.0 - Math.Cos(num1));
this._b2 = (float) ((1.0 - Math.Cos(num1)) / 2.0);
this._a0 = (float) (1.0 + num2);
this._a1 = (float) (-2.0 * Math.Cos(num1));
this._a2 = (float) (1.0 - num2);
break;
case IirFilterType.HighPass:
this._b0 = (float) ((1.0 + Math.Cos(num1)) / 2.0);
this._b1 = (float) -(1.0 + Math.Cos(num1));
this._b2 = (float) ((1.0 + Math.Cos(num1)) / 2.0);
this._a0 = (float) (1.0 + num2);
this._a1 = (float) (-2.0 * Math.Cos(num1));
this._a2 = (float) (1.0 - num2);
break;
case IirFilterType.Notch:
this._b0 = 1f;
this._b1 = (float) (-2.0 * Math.Cos(num1));
this._b2 = 1f;
this._a0 = (float) (1.0 + num2);
this._a1 = (float) (-2.0 * Math.Cos(num1));
this._a2 = (float) (1.0 - num2);
break;
default:
this._b0 = (float) num2;
this._b1 = 0.0f;
this._b2 = (float) -num2;
this._a0 = (float) (1.0 + num2);
this._a1 = (float) (-2.0 * Math.Cos(num1));
this._a2 = (float) (1.0 - num2);
break;
}
this._b0 /= this._a0;
this._b1 /= this._a0;
this._b2 /= this._a0;
this._a1 /= this._a0;
this._a2 /= this._a0;
this._x1 = 0.0f;
this._x2 = 0.0f;
this._y1 = 0.0f;
this._y2 = 0.0f;
}
static IirFilter AnalogPrototypeToDigitalFilter(ZeroPoleGain analogPrototype, Pair<double,double> cornerFreqs, BandType bandType, IirFilterType filterType)
{
// Check that we have valid frequencies
bool isError = false;
isError |= (cornerFreqs.First < 0 || cornerFreqs.First > Math.PI);
if(bandType == BandType.BandPass || bandType == BandType.BandStop)
{
isError |= (cornerFreqs.Second < 0 || cornerFreqs.Second > Math.PI);
}
if (isError)
throw new Exception("Frequencies must be between 0 and PI inclusive");
//Prewarp the corner frequencies
//Assuming sampling frequency of 1/2 so that we don't need to account for sampling frequency when converting from analog to digital.
const double samplingFreq = 0.5;
Func<double, double> freqWarp = x => 2 * samplingFreq * Math.Tan(x/2);
Pair<double, double> warpedCornerFreqs = new Pair<double, double>();
warpedCornerFreqs.First = freqWarp(cornerFreqs.First);
warpedCornerFreqs.Second = freqWarp(cornerFreqs.Second);
// Set prototype to desired band
ZeroPoleGain analogFilter;
switch (bandType)
{
case BandType.LowPass:
analogFilter = FilterModifiers.AnalogPrototypeToLowPass(warpedCornerFreqs.First, analogPrototype);
break;
case BandType.HighPass:
analogFilter = FilterModifiers.AnalogPrototypeToHighPass(warpedCornerFreqs.First, analogPrototype);
break;
case BandType.BandPass:
analogFilter = FilterModifiers.AnalogPrototypeToBandPass(warpedCornerFreqs.First, warpedCornerFreqs.Second, analogPrototype);
break;
case BandType.BandStop:
analogFilter = FilterModifiers.AnalogPrototypeToBandStop(warpedCornerFreqs.First, warpedCornerFreqs.Second, analogPrototype);
break;
default: Debug.Assert(false); throw new Exception();
}
//Convert analog (continuous) filter to digital (discrete) filter
ZeroPoleGain digitalFilter;
digitalFilter = FilterModifiers.ConvertAnalogToDigital(analogFilter);
//Convert digital filter into second-order sections
SosGain sosGain = FilterModifiers.ConvertZeroPoleToSosFilter(digitalFilter);
//Create filter and return it
return new IirFilter(sosGain);
}
public FloatIirFilter(IirFilterType filterType, float frequency, float sampleRate, int qualityFactor)
{
Init(filterType, frequency, sampleRate, qualityFactor);
}
