public static IEnumerable <string> CompareFilterWindowsPhaseResponse()
{
const float filterFrequency = 150;
const float frameSizeInS = (1f / filterFrequency) * 15;
const int sampleRate = 48000;
int windoSize = (int)(frameSizeInS * sampleRate);
var windows = new[] {
FFTWindowBuilder.Blackmann(windoSize),
FFTWindowBuilder.Hamming(windoSize),
FFTWindowBuilder.Hann(windoSize),
FFTWindowBuilder.Door(windoSize)
};
var phases = new float[windows.Length];
for (int i = 1; i < 300; i++)
{
var signal = SignalGenerator.Sinus(sampleRate, frameSizeInS, i, (float)(Math.PI / 2f)).ToArray();
for (int j = 0; j < windows.Length; j++)
{
GoertzelMag(signal, sampleRate, filterFrequency, windows[j], out phases[j]);
}
yield return($"{i};" + string.Join(";", phases.Select(r => r.ToString(CultureInfo.InvariantCulture))));
}
}
public static IEnumerable <string> CompareResponseWithNoiseLevel()
{
const float filterFrequency = 150;
const float frameSizeInS = 0.1f;
const int sampleRate = 48000;
var signal = SignalGenerator.Sinus(sampleRate, frameSizeInS, filterFrequency).ToArray();
var window = FFTWindowBuilder.Hann(signal.Length);
for (int i = 0; i <= 100; i++)
{
var noisedSignal = signal.AddNoise(i / 100f).ToArray();
var response = GoertzelMag(noisedSignal, sampleRate, filterFrequency, window, out _);
yield return($"{i};{response.ToString(CultureInfo.InvariantCulture)}");
}
}
public static IEnumerable <string> CompareFrameSizes()
{
const float filterFrequency = 150;
var frameSizesInS = new float[] { 0.1f, 0.5f };
var sampleRate = 48000;
var hammings = frameSizesInS.Select(fs => FFTWindowBuilder.Hamming((int)(fs * sampleRate))).ToArray();
var responses = new float[frameSizesInS.Length];
for (int i = 1; i < 300; i++)
{
for (int j = 0; j < frameSizesInS.Length; j++)
{
var signal = SignalGenerator.Sinus(sampleRate, frameSizesInS[j], i).ToArray();
responses[j] = GoertzelMag(signal, sampleRate, filterFrequency, hammings[j], out _);
}
yield return($"{i};" + string.Join(";", responses.Select(r => r.ToString(CultureInfo.InvariantCulture))));
}
}
public static IEnumerable <string> CompareSamplingRates()
{
const float filterFrequency = 150;
const float frameSizeInS = 0.1f;
var sampleRates = new[] { 600, 8000, 48000 };
var hammings = sampleRates.Select(sr => FFTWindowBuilder.Hamming((int)(sr * frameSizeInS))).ToArray();
var responses = new float[sampleRates.Length];
for (int i = 1; i < 300; i++)
{
for (int j = 0; j < sampleRates.Length; j++)
{
var signal = SignalGenerator.Sinus(sampleRates[j], frameSizeInS, i).ToArray();
responses[j] = GoertzelMag(signal, sampleRates[j], filterFrequency, hammings[j], out _);
}
yield return($"{i};" + string.Join(";", responses.Select(r => r.ToString(CultureInfo.InvariantCulture))));
}
}
public static CTCSSDecoder Create(float tone, int sampleRate)
{
if (!ValidTones.Contains(tone))
{
throw new ArgumentOutOfRangeException(nameof(tone), @"is not a valid CTCSS tone");
}
if (sampleRate <= 0)
{
throw new ArgumentOutOfRangeException(nameof(sampleRate), @"value must be greater than 0");
}
float binWidthInHz = CalculateBinWidthForTone(tone);
float numberOfSamplesForRequiredBinWidth = sampleRate / binWidthInHz;
float samplesRequiredForOnePEriod = sampleRate / tone;
int frameSize = (int)Math.Round(numberOfSamplesForRequiredBinWidth + (numberOfSamplesForRequiredBinWidth % samplesRequiredForOnePEriod));
var frequenciesOfInterest = new[] { tone - binWidthInHz, tone, tone + binWidthInHz };
var lowPass = new LowPassFilter(sampleRate, tone + 10);
var goertzel = Goertzel.Create(frameSize, sampleRate, FFTWindowBuilder.Hann(frameSize), lowPass.Process, frequenciesOfInterest);
return(new CTCSSDecoder(goertzel, frameSize, binWidthInHz));
}
