public static Complex[] BandPassFilterFactors(double lowPassFreq, double highPassFreq, double sampleFreq, int filterLength, int n)
{
var window = new HanningWindow();
var windowFilterFactors = window.WindowFactors(filterLength);
var low = LowPassFilterFactors(lowPassFreq, sampleFreq, filterLength);
var high = HighPassFilterFactors(highPassFreq, sampleFreq, filterLength);
var lowWindowed = new double[n];
var highWindowed = new double[n];
for (int i = 0; i < filterLength; i++)
{
lowWindowed[i] = low[i] * windowFilterFactors[i];
highWindowed[i] = high[i] * windowFilterFactors[i];
}
for (int i = filterLength; i < n; i++)
{
lowWindowed[i] = 0;
highWindowed[i] = 0;
}
var shiftNumberFilter = (filterLength - 1) / 2;
var lowShiftedFilter = lowWindowed.Take(shiftNumberFilter);
var lowFilteredTemp = lowWindowed.Skip(shiftNumberFilter).ToList();
lowFilteredTemp.AddRange(lowShiftedFilter);
lowWindowed = lowFilteredTemp.ToArray();
var highShiftedFilter = highWindowed.Take(shiftNumberFilter);
var highFilteredTemp = highWindowed.Skip(shiftNumberFilter).ToList();
highFilteredTemp.AddRange(highShiftedFilter);
highWindowed = highFilteredTemp.ToArray();
var lowComplex = FourierTransform.FFT(lowWindowed);
var highComplex = FourierTransform.FFT(highWindowed);
var bandPass = new Complex[n];
for (int i = 0; i < n; i++)
{
bandPass[i] = lowComplex[i] * highComplex[i];
}
return(bandPass);
}
