public void TestLowPass16()
{
const int order = 16;
const double fs = 31250d;
const double cutoffFrequency = 300d;
const double error = 1e-4;
var coeff = new LowPassButterworthCoefficients(order, fs, cutoffFrequency);
var chain = coeff.Calculate();
var expected = Helpers.LoadCsv(Resources.LowPass16).ToList();
var expectedGain = 3.444463173412853e-25;
Assert.AreEqual(1, chain.GetTransitionBands(fs).Count());
foreach (var f in chain.GetTransitionBands(fs))
{
Assert.AreEqual(f, cutoffFrequency, 1.0);
}
Assert.AreEqual(expected.Count, chain.Count);
for (int i = 0; i < expected.Count; i++)
{
Helpers.ValidateBiquad(expected[i], chain[i], error);
}
}
public void TestLowPass08()
{
const int order = 8;
const double fs = 44100d;
const double cutoffFrequency = 500d;
const double error = 1e-4;
var coeff = new LowPassButterworthCoefficients(order, fs, cutoffFrequency);
var chain = coeff.Calculate();
var expected = new[]
{
new Biquad(0.000000, 0.000000, 0.000000, 1.000000, -1.864749, 0.869491),
new Biquad(1.000000, 2.000000, 1.000000, 1.000000, -1.883460, 0.888249),
new Biquad(1.000000, 2.000000, 1.000000, 1.000000, -1.919040, 0.923920),
new Biquad(1.000000, 2.000000, 1.000000, 1.000000, -1.967605, 0.972608),
};
Assert.AreEqual(1, chain.GetTransitionBands(fs).Count());
foreach (var f in chain.GetTransitionBands(fs))
{
Assert.AreEqual(f, cutoffFrequency, 2.0);
}
Assert.AreEqual(expected.Length, chain.Count);
for (int i = 0; i < expected.Length; i++)
{
Helpers.ValidateBiquad(expected[i], chain[i], error);
}
}
public void TestLowPass2()
{
const int order = 2;
const double fs = 44100d;
const double cutoffFrequency = 2000d;
const double error = 1e-4;
var coeff = new LowPassButterworthCoefficients(order, fs, cutoffFrequency);
var chain = coeff.Calculate();
var expected = new[]
{
new Biquad(0.016819150107057118, 0.033638300214114236, 0.016819150107057118, 1, -1.6010923941836190, 0.66836899461184751),
};
Assert.AreEqual(1, chain.GetTransitionBands(fs).Count());
foreach (var f in chain.GetTransitionBands(fs))
{
Assert.AreEqual(f, cutoffFrequency, 5.0);
}
Assert.AreEqual(expected.Length, chain.Count);
for (int i = 0; i < expected.Length; i++)
{
Helpers.ValidateBiquad(expected[i], chain[i], error);
}
}
public void TestLowPassButtersworthFilteringWithDC()
{
const int order = 16;
const int fs = 44100;
const double cutoffFrequency = 2000d;
const int cycles = 10;
double[] frequencies = { 770, 5830 };
var validFrequencies = frequencies.TakeWhile(f => f < cutoffFrequency);
var coeff = new LowPassButterworthCoefficients(order, fs, cutoffFrequency);
TestFilterWithDC(order, fs, cycles, coeff, frequencies, validFrequencies, 1.0);
}
static void Main(string[] args)
{
const double noiseAmp = 1e-7d;
Console.WriteLine("Noise amplitude: {0}.", noiseAmp);
const double signalAmp = 0;
Console.WriteLine("Signal amplitude: {0}.", signalAmp);
const double signalFreq = 150;
Console.WriteLine("Signal frequency: {0} Hz.", signalFreq);
const double fs = 31250d;
Console.WriteLine("Sampling frequency: {0} Hz.", fs);
const double time = 0.15d;
Console.WriteLine("Analysis time: {0} s.", time);
const double lowCut = 5d;
Console.WriteLine("Filter low cut: {0} Hz.", lowCut);
const double highCut = 2000d;
Console.WriteLine("Filter high cut: {0} Hz.", highCut);
Console.WriteLine("Generating data...");
var samples = new float[(int)Math.Ceiling(fs * time)];
if (signalAmp > 0)
{
GenerateSinusoid(signalAmp, signalFreq, fs, samples);
}
if (noiseAmp > 0)
{
GenerateNoise(noiseAmp, samples);
}
Console.WriteLine("Designing filters...");
var lowPass = new LowPassButterworthCoefficients(5, fs, highCut).Calculate();
Console.WriteLine("Low pass filter:");
foreach (var biquad in lowPass)
{
Console.WriteLine(biquad);
}
var highPass = new HighPassButterworthCoefficients(3, fs, highCut).Calculate();
Console.WriteLine("High pass filter:");
foreach (var biquad in highPass)
{
Console.WriteLine(biquad);
}
Console.WriteLine("Processing data...");
var result = new float[samples.Length];
Array.Copy(samples, result, samples.Length);
lowPass.Filter(result, 0, result, 0, result.Length);
highPass.Filter(result, 0, result, 0, result.Length);
Console.WriteLine("Result:");
var min = double.MaxValue;
var max = double.MinValue;
var sum = 0d;
var sqsum = 0d;
for (int i = 0; i < result.Length; i++)
{
var value = result[i];
min = Math.Min(min, value);
max = Math.Max(max, value);
sum += value;
sqsum += value * value;
}
var mean = sum / result.Length;
var variance = (sqsum - result.Length * mean * mean) / (result.Length - 1);
Console.WriteLine("Minimum: {0}.", min);
Console.WriteLine("Maximum: {0}.", max);
Console.WriteLine("Mean value: {0}.", mean);
Console.WriteLine("Variance: {0}.", variance);
Console.WriteLine("Standard deviation: {0}.", Math.Sqrt(variance));
}