/// <summary>
/// Create a new group of filters.
/// </summary>
public Filters(FiltersType type, params FormattableString[] filters)
{
Type = type;
foreach (var filter in filters)
{
this.Add(new Filter(filter));
}
}
/// <summary>Set up a BiQuad Filter</summary>
/// <param name="type">filter type</param>
/// <param name="dbGain">gain of filter</param>
/// <param name="freq">center frequency</param>
/// <param name="srate">sampling rate</param>
/// <param name="bandwidth">bandwidth in octaves</param>
/// <returns>BiquadCoefficients pointer</returns>
public BiquadCoefficients *BiQuadFilter(FiltersType type, double dbGain, double freq,
double srate, double bandwidth)
{
BiquadCoefficients *pBiquad;
double a0, a1, a2, b0, b1, b2;
pBiquad = Alloc(sizeof(BiquadCoefficients));
if (pBiquad == null)
{
return(null);
}
// setup variables
double A = Math.Pow(10, dbGain / 40);
double omega = 2 * Math.PI * freq / srate;
double sinW0 = Math.Sin(omega);
double cosW0 = Math.Cos(omega);
double alpha = sinW0 * Math.Sinh(LN2 / 2 * bandwidth * omega / sinW0);
double beta = Math.Sqrt(A + A);
switch (type)
{
case FiltersType.LPF:
b0 = (1 - cosW0) / 2;
b1 = 1 - cosW0;
b2 = (1 - cosW0) / 2;
a0 = 1 + alpha;
a1 = -2 * cosW0;
a2 = 1 - alpha;
break;
case FiltersType.PEQ:
b0 = 1 + (alpha * A);
b1 = -2 * cosW0;
b2 = 1 - (alpha * A);
a0 = 1 + (alpha / A);
a1 = -2 * cosW0;
a2 = 1 - (alpha / A);
break;
case FiltersType.HSH:
b0 = A * ((A + 1) + (A - 1) * cosW0 + beta * sinW0);
b1 = -2 * A * ((A - 1) + (A + 1) * cosW0);
b2 = A * ((A + 1) + (A - 1) * cosW0 - beta * sinW0);
a0 = (A + 1) - (A - 1) * cosW0 + beta * sinW0;
a1 = 2 * ((A - 1) - (A + 1) * cosW0);
a2 = (A + 1) - (A - 1) * cosW0 - beta * sinW0;
break;
default:
Free(pBiquad);
return(null);
}
// precompute the coefficients
pBiquad->a0 = b0 / a0;
pBiquad->a1 = b1 / a0;
pBiquad->a2 = b2 / a0;
pBiquad->a3 = a1 / a0;
pBiquad->a4 = a2 / a0;
// zero initial samples
pBiquad->x1 = pBiquad->x2 = 0;
pBiquad->y1 = pBiquad->y2 = 0;
return(pBiquad);
}
/// <summary>Set up a BiQuad Filter</summary>
/// <param name="type">filter type</param>
/// <param name="dbGain">gain of filter</param>
/// <param name="freq">center frequency</param>
/// <param name="srate">sampling rate</param>
/// <param name="bandwidth">bandwidth in octaves</param>
/// <returns>BiquadCoefficients pointer</returns>
public BiquadCoefficients* BiQuadFilter(FiltersType type, double dbGain, double freq,
double srate, double bandwidth)
{
BiquadCoefficients* pBiquad;
double a0, a1, a2, b0, b1, b2;
pBiquad = Alloc(sizeof(BiquadCoefficients));
if (pBiquad == null)
return null;
// setup variables
double A = Math.Pow(10, dbGain / 40);
double omega = 2 * Math.PI * freq / srate;
double sinW0 = Math.Sin(omega);
double cosW0 = Math.Cos(omega);
double alpha = sinW0 * Math.Sinh(LN2 / 2 * bandwidth * omega / sinW0);
double beta = Math.Sqrt(A + A);
switch (type)
{
case FiltersType.LPF:
b0 = (1 - cosW0) / 2;
b1 = 1 - cosW0;
b2 = (1 - cosW0) / 2;
a0 = 1 + alpha;
a1 = -2 * cosW0;
a2 = 1 - alpha;
break;
case FiltersType.PEQ:
b0 = 1 + (alpha * A);
b1 = -2 * cosW0;
b2 = 1 - (alpha * A);
a0 = 1 + (alpha / A);
a1 = -2 * cosW0;
a2 = 1 - (alpha / A);
break;
case FiltersType.HSH:
b0 = A * ((A + 1) + (A - 1) * cosW0 + beta * sinW0);
b1 = -2 * A * ((A - 1) + (A + 1) * cosW0);
b2 = A * ((A + 1) + (A - 1) * cosW0 - beta * sinW0);
a0 = (A + 1) - (A - 1) * cosW0 + beta * sinW0;
a1 = 2 * ((A - 1) - (A + 1) * cosW0);
a2 = (A + 1) - (A - 1) * cosW0 - beta * sinW0;
break;
default:
Free(pBiquad);
return null;
}
// precompute the coefficients
pBiquad->a0 = b0 / a0;
pBiquad->a1 = b1 / a0;
pBiquad->a2 = b2 / a0;
pBiquad->a3 = a1 / a0;
pBiquad->a4 = a2 / a0;
// zero initial samples
pBiquad->x1 = pBiquad->x2 = 0;
pBiquad->y1 = pBiquad->y2 = 0;
return pBiquad;
}
