public void TestHighPass2()
{
const int order = 2;
const double fs = 44100d;
const double cutoffFrequency = 2000d;
const double error = 1e-4;
var coeff = new HighPassButterworthCoefficients(order, fs, cutoffFrequency);
var chain = coeff.Calculate();
var expected = new[]
{
new Biquad(0.817365347198867, -1.63473069439773, 0.817365347198867, 1, -1.60109239418362, 0.668368994611848),
};
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 TestHighPassButtersworthFilteringWithDC()
{
const int order = 16;
const int fs = 44100;
const double cutoffFrequency = 1000d;
const int cycles = 10;
double[] frequencies = { 330, 1870 };
var validFrequencies = frequencies.SkipWhile(f => f < cutoffFrequency);
var coeff = new HighPassButterworthCoefficients(order, fs, cutoffFrequency);
TestFilterWithDC(order, fs, cycles, coeff, frequencies, validFrequencies, 10.0);
}
public void TestHighPass16()
{
const int order = 16;
const double fs = 31250d;
const double cutoffFrequency = 100d;
const double error = 1e-4;
var coeff = new HighPassButterworthCoefficients(order, fs, cutoffFrequency);
var chain = coeff.Calculate();
var expected = Helpers.LoadCsv(Resources.HighPass16).ToList();
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);
}
}
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));
}
