Function ComputeSpectrum

libraries/lib-fft/Spectrum.cpp:22–123

using Floats = ArrayOf<float>;

bool ComputeSpectrum(
   const float* data, size_t width, size_t windowSize, float* output,
   bool autocorrelation, int windowFunc)
{
   if (width < windowSize)
      return false;

   if (!data || !output)
      return true;

   Floats processed{ windowSize };

   for (size_t i = 0; i < windowSize; i++)
      processed[i] = float(0.0);
   auto half = windowSize / 2;

   Floats in{ windowSize };
   Floats out{ windowSize };
   Floats out2{ windowSize };

   size_t start = 0;
   unsigned windows = 0;
   while (start + windowSize <= width) {
      for (size_t i = 0; i < windowSize; i++)
         in[i] = data[start + i];

      WindowFunc(windowFunc, windowSize, in.get());

      if (autocorrelation) {
         // Take FFT
         RealFFT(windowSize, in.get(), out.get(), out2.get());
         // Compute power
         for (size_t i = 0; i < windowSize; i++)
            in[i] = (out[i] * out[i]) + (out2[i] * out2[i]);

         // Tolonen and Karjalainen recommend taking the cube root
         // of the power, instead of the square root

         for (size_t i = 0; i < windowSize; i++)
            in[i] = powf(in[i], 1.0f / 3.0f);

         // Take FFT
         RealFFT(windowSize, in.get(), out.get(), out2.get());
      }
      else
         PowerSpectrum(windowSize, in.get(), out.get());

      // Take real part of result
      for (size_t i = 0; i < half; i++)
        processed[i] += out[i];

      start += half;
      windows++;
   }

   if (autocorrelation) {

      // Peak Pruning as described by Tolonen and Karjalainen, 2000