public IEnumerable <Point> Filtration(int M, double fo, IEnumerable <Point> points, IWindow window,
FilterType filterType)
{
var fp = 1 / (points.ElementAt(1).X - points.ElementAt(0).X);
if (filterType == FilterType.HighPassFilter)
{
fo = fp / 2 - fo;
}
var response = new List <Point>();
var K = fp / fo;
for (var i = 0; i < M; i++)
{
response.Add(new Point(i,
ImpulseResponse.Response(i, K, M) * window.Window(i, M) * filterTypes[filterType](i)));
}
var ret = Convolution.Convolute(points, response);
var amplitude = ret.Select(p => p.Y).Max() * 2;
amplitude = points.Select(p => p.Y).Max() / amplitude;
foreach (var point in ret)
{
point.Y *= amplitude;
}
return(ret);
}
/// <summary>
/// Create a filter to remove low frequencies in online processing scenarios.
/// </summary>
public static OnlineFilter CreateHighpass(ImpulseResponse mode, double sampleRate, double cutoffRate)
{
return(CreateHighpass(
mode,
sampleRate,
cutoffRate,
mode == ImpulseResponse.Finite ? 64 : 4)); // order
}
/// <summary>
/// Create a filter to remove middle (all but low and high) frequencies in online processing scenarios.
/// </summary>
public static OnlineFilter CreateBandstop(ImpulseResponse mode, double sampleRate, double cutoffLowRate, double cutoffHighRate)
{
return(CreateBandstop(
mode,
sampleRate,
cutoffLowRate,
cutoffHighRate,
mode == ImpulseResponse.Finite ? 64 : 4)); // order
}
/// <summary>
/// Create a filter to remove low and high frequencies in online processing scenarios.
/// </summary>
public static OnlineFilter CreateBandpass(ImpulseResponse mode, double sampleRate, double cutoffLowRate, double cutoffHighRate)
{
return CreateBandpass(
mode,
sampleRate,
cutoffLowRate,
cutoffHighRate,
mode == ImpulseResponse.Finite ? 64 : 4); // order
}
/// <summary>
/// Samples the input stream and applies a high-pass filter (using MathNet.Filtering) over the sampled input stream. Removes low frequencies.
/// </summary>
/// <param name="input">The input source of doubles.</param>
/// <param name="sampleRate">The desired sample rate for the filter.</param>
/// <param name="cutoffRate">The desired cutoff for the filter.</param>
/// <param name="impulseResponse">Specifies how the filter will respond to an impulse input (Finite or Infinite). Default is Finite.</param>
/// <param name="sampleInterpolator">Optional sampling interpolator over the input. Default is a reproducible linear interpolation.</param>
/// <param name="alignmentDateTime">If non-null, this parameter specifies a time to align the sampled messages with, and the sampled messages
/// will have originating times that align with (i.e., are an integral number of intervals away from) the specified alignment time.</param>
/// <param name="deliveryPolicy">An optional delivery policy for the input stream.</param>
/// <returns>A high-pass filtered version of the input.</returns>
public static IProducer <double> HighpassFilter(
this IProducer <double> input,
double sampleRate,
double cutoffRate,
ImpulseResponse impulseResponse = ImpulseResponse.Finite,
Interpolator <double, double> sampleInterpolator = null,
DateTime?alignmentDateTime = null,
DeliveryPolicy <double> deliveryPolicy = null)
{
var filter = OnlineFilter.CreateHighpass(impulseResponse, sampleRate, cutoffRate);
return(MathNetFilter(input, sampleRate, sampleInterpolator ?? Reproducible.Linear(), alignmentDateTime, filter, deliveryPolicy));
}
CreateLowpass(
ImpulseResponse mode,
double sampleRate,
double cutoffRate
)
{
return(CreateLowpass(
mode,
sampleRate,
cutoffRate,
mode == ImpulseResponse.Finite ? 64 : 4 // order
));
}
CreateBandstop(
ImpulseResponse mode,
double sampleRate,
double cutoffLowRate,
double cutoffHighRate
)
{
return(CreateBandstop(
mode,
sampleRate,
cutoffLowRate,
cutoffHighRate,
mode == ImpulseResponse.Finite ? 64 : 4 // order
));
}
/// <summary>
/// Create a filter to remove middle (all but low and high) frequencies in online processing scenarios.
/// </summary>
public static OnlineFilter CreateBandstop(ImpulseResponse mode, double sampleRate, double cutoffLowRate, double cutoffHighRate, int order)
{
if (mode == ImpulseResponse.Finite)
{
double[] c = FirCoefficients.BandStop(sampleRate, cutoffLowRate, cutoffHighRate, order >> 1);
return(new OnlineFirFilter(c));
}
if (mode == ImpulseResponse.Infinite)
{
double[] c = IirCoefficients.BandStop(sampleRate, cutoffLowRate, cutoffHighRate);
return(new OnlineIirFilter(c));
}
throw new ArgumentException("mode");
}
/// <summary>
/// Create a filter to remove middle (all but low and high) frequencies in online processing scenarios.
/// </summary>
public static OnlineFilter CreateBandstop(ImpulseResponse mode, double sampleRate, double cutoffLowRate, double cutoffHighRate, int order)
{
if (mode == ImpulseResponse.Finite)
{
double[] c = FirCoefficients.BandStop(sampleRate, cutoffLowRate, cutoffHighRate, order >> 1);
return new OnlineFirFilter(c);
}
if (mode == ImpulseResponse.Infinite)
{
double[] c = IirCoefficients.BandStop(sampleRate, cutoffLowRate, cutoffHighRate);
return new OnlineIirFilter(c);
}
throw new ArgumentException("mode");
}
/// <summary>
/// Create a filter to remove low frequencies in online processing scenarios.
/// </summary>
public static OnlineFilter CreateHighpass(ImpulseResponse mode, double sampleRate, double cutoffRate, int order)
{
if (mode == ImpulseResponse.Finite)
{
double[] c = FirCoefficients.HighPass(sampleRate, cutoffRate, order >> 1);
return(new OnlineFirFilter(c));
}
if (mode == ImpulseResponse.Infinite)
{
// TODO: investigate (bandwidth)
double[] c = IirCoefficients.HighPass(sampleRate, cutoffRate, cutoffRate);
return(new OnlineIirFilter(c));
}
throw new ArgumentException("mode");
}
CreateBandpass(
ImpulseResponse mode,
double sampleRate,
double cutoffLowRate,
double cutoffHighRate,
int order
)
{
if (mode == ImpulseResponse.Finite)
{
double[] c = FIR.FirCoefficients.BandPass(sampleRate, cutoffLowRate, cutoffHighRate, order >> 1);
return(new FIR.OnlineFirFilter(c));
}
if (mode == ImpulseResponse.Infinite)
{
double[] c = IIR.IirCoefficients.BandPass(sampleRate, cutoffLowRate, cutoffHighRate);
return(new IIR.OnlineIirFilter(c));
}
throw new ArgumentException("mode");
}
/// <summary>
/// Create a filter to remove high frequencies in online processing scenarios.
/// </summary>
public static OnlineFilter CreateLowpass(ImpulseResponse mode, double sampleRate, double cutoffRate, int order)
{
if (mode == ImpulseResponse.Finite)
{
double[] c = FirCoefficients.LowPass(sampleRate, cutoffRate, order >> 1);
return new OnlineFirFilter(c);
}
if (mode == ImpulseResponse.Infinite)
{
// TODO: investigate (bandwidth)
double[] c = IirCoefficients.LowPass(sampleRate, cutoffRate, cutoffRate);
return new OnlineIirFilter(c);
}
throw new ArgumentException("mode");
}