[Discuss-gnuradio] Geortzel DFT implementation checked in

[Johnathan Corgan]

Checked in to CVS are a C++ implementation and stream processing block
for the Goertzel single-bin DFT transform.

The C++ class constructor takes the sample rate, length of the Goertzel
block, and the frequency of the bin of interest:

gri_goertzel::gri_goertzel(int rate, int points, float freq);

The frequency does not have to be "centered on a bin" such as when doing
a standard DFT.

By calling the dft member function with a pointer to an array of floats,
one receives the real and imaginary parts of the DFT transform of the
array for the frequency specified in the constructor:

gr_complex gri_goertzel::dft(float *input);

Wrapped around this is a signal processing block that accepts a
real-valued stream of floats and outputs a complex stream of DFT
outputs, at a rate equal to the input rate / length of the Goertzel
transform:

gr.goertzel_fc(rate, points, freq)

Basic testing with a variety of inputs shows correct functioning but no
automated QA script is in place yet.

The C++ class will be used as part of the planned gr.ctcss_squelch() block.

-Johnathan, AE6HO