public void LowPass()
{
const double passbandFreq = 2000 / _SamplingFrequency;
const double stopbandFreq = 2500 / _SamplingFrequency;
const double passbandRipple = 5;
const double stopbandAttenuation = 6;
var(eb, ea) = IirCoefficients.LowPass(passbandFreq, stopbandFreq, passbandRipple, stopbandAttenuation);
var b = eb.ToArray();
var a = ea.ToArray();
var desiredB = new double[] { 0.09723679451225617, 0.09723679451225617 };
var desiredA = new double[] { 1, -0.8055264109754877 };
Assert.AreEqual(desiredB.Length, b.Length);
Assert.AreEqual(desiredA.Length, a.Length);
for (int i = 0; i < b.Length; i++)
{
Assert.AreEqual(desiredB[i], b[i], _Tolerance);
}
for (int i = 0; i < a.Length; i++)
{
Assert.AreEqual(desiredA[i], a[i], _Tolerance);
}
}
/// <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");
}
