public void TestBandStop16()
{
const int order = 16;
const double fs = 31250d;
const double cutoffFrequency = 60;
const double br = 1;
const double error = 1e-3;
var coeff = new BandStopButterworthCoefficients(order, fs, cutoffFrequency - br, cutoffFrequency + br);
var chain = coeff.Calculate();
Assert.AreEqual(2, chain.GetTransitionBands(fs).Count());
foreach (var f in chain.GetTransitionBands(fs))
{
Assert.IsTrue(Math.Abs(cutoffFrequency - br - f) <= 2.0 || Math.Abs(cutoffFrequency + br - f) <= 1.0);
}
var expected = Helpers.LoadCsv(Resources.BandStop16).ToList();
var expectedGain = 0.997950883359409;
Assert.AreEqual(expected.Count, chain.Count);
for (int i = 0; i < expected.Count; i++)
{
Helpers.ValidateBiquad(expected[i], chain[i], error);
}
}
public void TestBandStop2()
{
const int order = 2;
const double fs = 44100d;
const double cutoffFrequency = 2000;
const double br = 1720;
const double error = 1e-3;
var coeff = new BandStopButterworthCoefficients(order, fs, cutoffFrequency - br, cutoffFrequency + br);
var chain = coeff.Calculate();
Assert.AreEqual(2, chain.GetTransitionBands(fs).Count());
foreach (var f in chain.GetTransitionBands(fs))
{
Assert.IsTrue(Math.Abs(cutoffFrequency - br - f) <= 2.0 || Math.Abs(cutoffFrequency + br - f) <= 5.0);
}
var expected = new[]
{
new Biquad(0.706107, -1.397005, 0.706107, 1.000000, -1.343380, 0.528841),
new Biquad(1.000000, -1.978461, 1.000000, 1.000000, -1.944714, 0.946480),
};
Assert.AreEqual(expected.Length, chain.Count);
for (int i = 0; i < expected.Length; i++)
{
Helpers.ValidateBiquad(expected[i], chain[i], error);
}
}
public void TestBandStopButtersworthFilteringWithDC()
{
const int order = 16;
const int fs = 44100;
const double f1 = 500d;
const double f2 = 8000d;
const int cycles = 10;
double[] frequencies = { 330, 770, 1870, 5830, 9790 };
var validFrequencies = frequencies.TakeWhile(f => f < f1).Concat(frequencies.SkipWhile(f => f < f2));
var coeff = new BandStopButterworthCoefficients(order, fs, f1, f2);
TestFilterWithDC(order, fs, cycles, coeff, frequencies, validFrequencies, -10.0);
}
public void TestBandStopSinusoid()
{
const int order = 16;
const int fs = 44100;
const int targetFrequency = 3;
const double br = 5;
const int cycles = 10;
double[] frequencies =
{ 65.406, 130.81, 261.63, 523.25, 1046.5, 2093.0, 4186.0, 8372.0 };
var signal = new double[cycles * fs];
foreach (var frequency in frequencies)
{
Helpers.GenerateSinusoid(frequency, fs, signal);
}
var im = new double[signal.Length];
var coeff = new BandStopButterworthCoefficients(order, fs, frequencies[targetFrequency] - br, frequencies[targetFrequency] + br);
var chain = coeff.Calculate();
chain.Filter(signal, 0, signal, 0, signal.Length);
var count = signal.Length / 2;
FourierTransform2.FFT(signal, im, FourierTransform.Direction.Forward);
Helpers.CalculateEnergy(signal, im, count);
var maxEnergy = signal.Take(count).Max();
var step = fs / (2d * count);
var peakSet = new HashSet <double>();
for (int i = 1; i < count - 1; i++)
{
var freq = i * step;
if (signal[i] > signal[i - 1] && signal[i] > signal[i + 1] && signal[i] >= 0.01 * maxEnergy)
{
var peak = frequencies.FirstOrDefault(x => Math.Abs(freq - x) <= 1);
Assert.AreNotEqual(0, peak);
peakSet.Add(peak);
}
}
Assert.IsTrue(peakSet.SetEquals(frequencies.Except(Enumerable.Repeat(frequencies[targetFrequency], 1))));
}
