// calculate the power spectrum of the incoming signal stored in data field by estimating linear model and applying the lookupTable on the model
public double[] estimatePowerSpectrum()
{
// init power spectrum
double[] powerSpectrum = new double[numBins];
// if filter is constructed properly and data filed is filled with suitable data
if (allowRun && data != null && linModel != null)
{
// init variables
int counter = 0; // counter to fill powerspectrum array
// multiply power by a factor of sqrt(2) to account for positive and negative frequencies.
linModel = linModel * Math.Sqrt(2.0);
// perform power spectrum estimation: cycle through bins, per bin calculate for each sample, ie frequencyresolution. (in BCI2000 this was transferspectrum.evaluate function, based loosely on function evlmem in Press et al.)
for (int bin = 0; bin < numBins; ++bin)
{
// init
powerSpectrum[bin] = 0.0;
int evalInBin = (int)bins[bin, 2];
// cycle through samples per bin
for (int eval = 0; eval < evalInBin; eval++)
{
// get power estimate for given frequency in lookupTable and store in power spectrum output array
Complex valueComplex = linModel.evaluate(lookupTable[counter]);
powerSpectrum[bin] += ((valueComplex.Real * valueComplex.Real) + (valueComplex.Imaginary * valueComplex.Imaginary)); // it's actually the squared magnitude rather than a norm
counter++;
}
// normalize spectral power to frequency resolution
powerSpectrum[bin] /= evalInBin;
// divide by two and take square root to get amplitudes
powerSpectrum[bin] = Math.Sqrt(powerSpectrum[bin] / 2);
}
// output power spectrum estimation
//logger.Debug("Power spectrum estimation of data:");
//logger.Debug("Frequency bin \t Power");
//for (int i = 0; i < numBins; i++) {
// double startBin = (firstBinCenter + (binWidth * i)) - (binWidth / 2);
// double endBin = (firstBinCenter + (binWidth * i)) + (binWidth / 2);
// logger.Debug("{0} - {1} Hz \t {2}", startBin, endBin, powerSpectrum[i]);
//}
}
else
{
logger.Error("ARFilter is not constructed properly or input data is not suitable. Power spectrum can not be determined. See log files for more information.");
}
// return powerspectrum
return(powerSpectrum);
}
