public static void Example7() //================[ Basic FFT + Windowing Example + ZeroPadding ]================
{
// Same Input Signal as Example 1, except everything is a power of two
double amplitude = 1.0; double frequency = 32768;
UInt32 length = 1024; double samplingRate = 131072;
double[] inputSignal = DSP.Generate.ToneSampling(amplitude, frequency, samplingRate, length);
// Apply window to the Input Data & calculate Scale Factor
double[] wCoefs = DSP.Window.Coefficients(DSP.Window.Type.Hamming, length);
double[] wInputData = DSP.Math.Multiply(inputSignal, wCoefs);
double wScaleFactor = DSP.Window.ScaleFactor.Signal(wCoefs);
// Instantiate & Initialize a new DFT
DSPLib.FFT fft = new DSPLib.FFT();
fft.Initialize(length, length * 3); // Zero Padding = 1024 * 3
// Call the FFT and get the scaled spectrum back
Complex[] cSpectrum = fft.Execute(wInputData);
// Convert the complex spectrum to note: Magnitude Squared Format
// See text for the reasons to use Mag^2 format.
double[] lmSpectrum = DSP.ConvertComplex.ToMagnitude(cSpectrum);
// Properly scale the spectrum for the added window
lmSpectrum = DSP.Math.Multiply(lmSpectrum, wScaleFactor);
// For plotting on an XY Scatter plot generate the X Axis frequency Span
double[] freqSpan = fft.FrequencySpan(samplingRate);
// At this point a XY Scatter plot can be generated from,
// X axis => freqSpan
// Y axis => lmSpectrum
}
/// <summary>
/// FFT using DSPLib library.
/// </summary>
/// <param name="inputArray">The input array.</param>
/// <param name="logScale">if set to <c>true</c> [log scale]</param>
/// <returns></returns>
Tuple <double[], double[]> FastFourierDSPLib(double[] inputArray, bool logScale)
{
double[] tempArray = new double[2048];
for (int i = 0; i < 2048; i++)
{
tempArray[i] = inputArray[i];
}
UInt32 length = 2048;
double samplingRate = 44100;
double[] spectrum = new double[4096];
double[] wCoefs = DSP.Window.Coefficients(DSP.Window.Type.Hamming, length);
double[] wInputData = DSP.Math.Multiply(tempArray, wCoefs);
double wScaleFactor = DSP.Window.ScaleFactor.Signal(wCoefs);
DSPLib.FFT fft = new DSPLib.FFT();
fft.Initialize(length, length * 3);
Complex[] cSpectrum = fft.Execute(wInputData);
spectrum = DSP.ConvertComplex.ToMagnitude(cSpectrum);
if (logScale == true)
{
spectrum = DSP.ConvertMagnitude.ToMagnitudeDBV(spectrum);
for (int i = 0; i < spectrum.Length; i++)
{
spectrum[i] -= 51;
}
}
spectrum = DSP.Math.Multiply(spectrum, wScaleFactor);
double[] freqSpan = fft.FrequencySpan(samplingRate);
var tuple = new Tuple <double[], double[]>(spectrum, freqSpan);
return(tuple);
}