Frequency extraction

Question

how to extract the frequency spectrum from a set of discrete data using fft

Answer 1

Perhaps using an existing library, like FFTW.

Answer 2

Another resource with downloadable C source is Introduction To Signal Processing

Answer 3

Do you have to do it in C, they're probably easier through MATLAB

Answer 4

Are you looking to build your own FFT calculation for homework? What is the aim? There is very little that we can go by here so no one is going to write out any code for you. I can say that it's a good learning experience for numerical work.

It'd be interesting (for the benefit of yourself, this has been done to death) to compare the performance of your chosen implementation with a typical radix-2 FFT algorithm from FFTW or elsewhere.