This project contains a simple FFT implementation by C#.
long size = 4096;
Complex[] signal = new Complex[size];
Complex[] spectrum = new Complex[size];
FFTCalculator fft = new FFTCalculator(size);
// Do an FFT: spectrum = FFT(signal)
fft.DFT(signal, spectrum);
// Do an IFFT: signal = IFFT(spectrum)
fft.IDFT(spectrum, signal);