FFT

I have wasted to much time trying to write a DFT algoritm in C, source code can be found here. It's not very good, but it computes correctly. Here is an example, where I put in a noisy signal, it contains three sine signals, with frequencies 2Hz, 17Hz and 401Hz with different amplitudes and some noise. It looks like this

And after the Fourier Transform i get this data

In the code I simply checked which frequencies was larger than 0.35 in amplitude, and saved them. The other ones was zeroed. After and inverse fourier transform with the ifft() function. The output was this.

Pretty :)