protected internal override IOnlineFilter CreateBandStop(FilterDesignSettings settings, double lowFrequency, double highFrequency)
{
return Create(Design(FilterKind.BandStop, settings.Order,
CalculateRipple(settings),
settings.NormalizeFrequency(lowFrequency),
settings.NormalizeFrequency(highFrequency)));
}
protected internal override IOnlineFilter CreateNotch(FilterDesignSettings settings, double frequency)
{
const double notchHalfWidth = 0.5; // Hz
return Create(Design(FilterKind.BandStop, settings.Order,
CalculateRipple(settings),
settings.NormalizeFrequency(frequency - notchHalfWidth),
settings.NormalizeFrequency(frequency + notchHalfWidth)));
}
protected internal override IOnlineFilter CreateOther(FilterDesignSettings settings)
{
int windowSize = settings.Order > 0 ? settings.Order : MedianFilterDesignSettings.DefaultWindowSize;
var medianSettings = settings as MedianFilterDesignSettings;
if (medianSettings != null)
{
windowSize = medianSettings.WindowSize;
}
return(new Filter(windowSize));
}
private static T Resolve <T>(FilterDesignSettings settings, Func <RbjFilterDesignSettings, T> selector, T defaultValue)
{
Debug.Assert(selector != null);
var rbjSettings = settings as RbjFilterDesignSettings;
if (rbjSettings != null)
{
return(selector(rbjSettings));
}
return(defaultValue);
}
protected internal override IOnlineFilter CreateNotch(FilterDesignSettings settings, double frequency)
{
Debug.Assert(settings != null);
Debug.Assert(settings.SamplingRate > 0);
double omega = (2 * Math.PI) * (frequency / settings.SamplingRate);
double tsin = Math.Sin(omega);
double tcos = Math.Cos(omega);
double alpha = tsin / (2 * Resolve(settings, x => x.Quality, RbjFilterDesignSettings.DefaultQuality));
double b0 = 1;
double b1 = -2 * tcos;
double b2 = 1;
double a0 = 1 + alpha;
double a1 = -2 * tcos;
double a2 = 1 - alpha;
return(CreateCascade(settings.Order, new IirFilterCoefficients {
B = new double[] { b0, b1, b2 }, A = new double[] { a0, a1, a2 }
}));
}
protected internal override IOnlineFilter CreateHighShelf(FilterDesignSettings settings, double frequency)
{
Debug.Assert(settings != null);
Debug.Assert(settings.SamplingRate > 0);
double omega = (2 * Math.PI) * (frequency / settings.SamplingRate);
double tsin = Math.Sin(omega);
double tcos = Math.Cos(omega);
double alpha = tsin / (2 * Resolve(settings, x => x.Quality, RbjFilterDesignSettings.DefaultQuality));
double a = Math.Pow(10, Resolve(settings, x => x.Gain, RbjFilterDesignSettings.DefaultGain) / 40);
double w0 = Math.PI * 2 * frequency / settings.SamplingRate;
double b0 = a * ((a + 1) + (a - 1) * Math.Cos(w0) + 2 * Math.Sqrt(a) * alpha);
double b1 = -2 * a * ((a - 1) + (a + 1) * Math.Cos(w0));
double b2 = a * ((a + 1) + (a - 1) * Math.Cos(w0) - 2 * Math.Sqrt(a) * alpha);
double a0 = (a + 1) - (a - 1) * Math.Cos(w0) + 2 * Math.Sqrt(a) * alpha;
double a1 = 2 * ((a - 1) - (a + 1) * Math.Cos(w0));
double a2 = (a + 1) - (a - 1) * Math.Cos(w0) - 2 * Math.Sqrt(a) * alpha;
return(CreateCascade(settings.Order, new IirFilterCoefficients {
B = new double[] { b0, b1, b2 }, A = new double[] { a0, a1, a2 }
}));
}
protected internal override IOnlineFilter CreateBandStop(FilterDesignSettings settings, double lowFrequency, double highFrequency)
{
Debug.Assert(settings != null);
Debug.Assert(settings.SamplingRate > 0);
double frequency = CalculateCenterFrequency(lowFrequency, highFrequency);
double q = CalculateQ(lowFrequency, highFrequency);
double omega = (2 * Math.PI) * (frequency / settings.SamplingRate);
double tsin = Math.Sin(omega);
double tcos = Math.Cos(omega);
double alpha = tsin / (2 * q);
double b0 = 1;
double b1 = -2 * tcos;
double b2 = 1;
double a0 = 1 + alpha;
double a1 = -2 * tcos;
double a2 = 1 - alpha;
return(CreateCascade(settings.Order, new IirFilterCoefficients {
B = new double[] { b0, b1, b2 }, A = new double[] { a0, a1, a2 }
}));
}
protected virtual double CalculateRipple(FilterDesignSettings settings)
{
// Default to 0 because most filters don't use Ripple
return 0;
}
protected internal override IOnlineFilter CreateHighPass(FilterDesignSettings settings, double frequency)
{
return Create(Design(FilterKind.HighPass, settings.Order,
CalculateRipple(settings),
settings.NormalizeFrequency(frequency)));
}
protected internal override IOnlineFilter CreateOther(FilterDesignSettings settings)
{
throw new NotImplementedException();
}
protected override double CalculateRipple(FilterDesignSettings settings)
{
return(settings.GetOrDefault <ChebyshevFilterDesignSettings, double>(x => x.MaximumRipple ?? -10, -10));
}
