public void TestLowPass08()
{
const int order = 8;
const double fs = 44100d;
const double cutoffFrequency = 500d;
const double error = 1e-4;
var coeff = new LowPassButtersworthCoefficients(order, fs, cutoffFrequency);
var chain = coeff.Calculate();
var expected = new[]
{
new Biquad(1, 2, 1, 1, -1.96762058043629, 0.97261960500367),
new Biquad(1, 2, 1, 1, -1.91907529383978, 0.92395098208778),
new Biquad(1, 2, 1, 1, -1.88350864178159, 0.88829396780773),
new Biquad(1, 2, 1, 1, -1.86480445083537, 0.86954225616013),
};
var expectedGain = 2.158589092625337e-12;
Assert.AreEqual(expectedGain, chain.Gain, error);
Assert.AreEqual(expected.Length, chain.Count);
for (int i = 0; i < expected.Length; i++)
{
Helpers.ValidateBiquad(expected[i], chain[i], error);
}
}
public override void ProcessSignal(float[] signal, float freqSampling)
{
var coeff = new LowPassButtersworthCoefficients(FilterOrder, freqSampling, CutOffFrequency);
var chain = coeff.Calculate();
// in place filtering
if (ZeroPhase)
{
chain.Filter(signal, 0, signal, 0, signal.Length);
}
else
{
chain.FilterOnce(signal, 0, signal, 0, signal.Length);
}
}
public void TestLowPassSinusoid()
{
const int order = 16;
const int fs = 44100;
const double cutoffFrequency = 400d;
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 LowPassButtersworthCoefficients(order, fs, cutoffFrequency);
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] >= 0.001 * maxEnergy)
{
var peak = frequencies.FirstOrDefault(x => Math.Abs(freq - x) <= 1);
Assert.AreNotEqual(0, peak);
peakSet.Add(peak);
}
}
Assert.IsTrue(peakSet.SetEquals(frequencies.Where(x => x < cutoffFrequency)));
}
public void TestLowPass16()
{
const int order = 16;
const double fs = 31250d;
const double cutoffFrequency = 300d;
const double error = 1e-4;
var coeff = new LowPassButtersworthCoefficients(order, fs, cutoffFrequency);
var chain = coeff.Calculate();
var expected = Helpers.LoadScript(Resources.LowPass16).Reverse().ToList();
var expectedGain = 3.444463173412853e-25;
Assert.AreEqual(expectedGain, chain.Gain, error);
Assert.AreEqual(expected.Count, chain.Count);
for (int i = 0; i < expected.Count; i++)
{
Helpers.ValidateBiquad(expected[i], chain[i], error);
}
}
public void TestLowPass12()
{
const int order = 12;
const double fs = 32000d;
const double cutoffFrequency = 2000d;
const double error = 1e-2;
var coeff = new LowPassButtersworthCoefficients(order, fs, cutoffFrequency);
var chain = coeff.Calculate();
var expected = Helpers.LoadScript(Resources.LowPass12).Reverse().ToList();
var expectedGain = 7.343036284781901e-10;
Assert.AreEqual(expectedGain, chain.Gain, error);
Assert.AreEqual(expected.Count, chain.Count);
for (int i = 0; i < expected.Count; i++)
{
Helpers.ValidateBiquad(expected[i], chain[i], error);
}
}
