/// <summary>Single thread DFT function.</summary>
/// <param name="start">The start index in the samples array.</param>
/// <param name="end">The end index in the samples array.</param>
private void dftSingle(long start, long end)
{
long N = end - start;
fourierSamples = new ComplexNum[N];
applyWindowing(start, N);
for (long f = 0; f < N; f++)
{
fourierSamples[f] = new ComplexNum();
for (int t = 0; t < N; t++)
{
fourierSamples[f].Re += windowingSamples[t] * Math.Cos((2 * Math.PI * t * f) / N);
fourierSamples[f].Im -= windowingSamples[t] * Math.Sin((2 * Math.PI * t * f) / N);
}
if (Math.Abs(fourierSamples[f].Re) < zeroThreshold)
{
fourierSamples[f].Re = 0.0;
}
if (Math.Abs(fourierSamples[f].Im) < zeroThreshold)
{
fourierSamples[f].Im = 0.0;
}
}
}
/// <summary>Generates a filter to filter out aliases for upsampling/downsampling.</summary>
/// <param name="newSampleRate">The new sample rate to determine the nyquist limit.</param>
/// <param name="csData">The sample data.</param>
/// <returns>ComplexNum array representing the filter.</returns>
private ComplexNum[] genSampleFilter(int newSampleRate, ClipboardData csData)
{
ComplexNum[] filter = new ComplexNum[csData.Cs.Length / 10];
int freq = newSampleRate / 2;
int bin = (freq * filter.Length) / newSampleRate;
for (int i = 0; i < filter.Length; ++i)
{
filter[i] = new ComplexNum();
if (i <= bin)
{
filter[i].Re = 1.0;
filter[i].Im = 1.0;
}
else
{
filter[i].Re = 0.0;
filter[i].Im = 0.0;
}
}
return(filter);
}
/// <summary>Thread proc for multithread DFT</summary>
/// <param name="threadIndex">Index of the thread.</param>
/// <param name="startRawSamples">The start index in the raw samples array.</param>
/// <param name="N">The total number of samples with which DFT is being applied to.</param>
/// <param name="chunkSize">Size of this threads chunk.</param>
private void dftThreadProc(int threadIndex, long startRawSamples, long N, long chunkSize)
{
ComplexNum[] dftSamples = new ComplexNum[chunkSize];
for (long f = 0; f < chunkSize; f++)
{
dftSamples[f] = new ComplexNum();
for (int t = 0; t < N; t++)
{
dftSamples[f].Re += windowingSamples[t] * Math.Cos((2 * Math.PI * t * (f + (threadIndex * chunkSize))) / N);
dftSamples[f].Im -= windowingSamples[t] * Math.Sin((2 * Math.PI * t * (f + (threadIndex * chunkSize))) / N);
}
if (Math.Abs(dftSamples[f].Re) < zeroThreshold)
{
dftSamples[f].Re = 0.0;
}
if (Math.Abs(dftSamples[f].Im) < zeroThreshold)
{
dftSamples[f].Im = 0.0;
}
}
dftThreadSamples[threadIndex] = dftSamples;
}