## Calculating a real-number FFT with FFTW3

In this article I’m going to explain how to calculate a real-number based FFT using FFTW, providing the source code. First, though, I will introduce some important concepts. Then I will provide code with comments within it. I will also provide a header containing sample data from a single channel sound file whose frames have been converted into double values. The samples are of a 440 Hz sine tone mixed with noise. I exported the raw sound data from Audacity, and used the od program (GNU coreutils), to convert the raw data to double precision floating point numbers, and outputted that into a file that I could reformat into the header, “a_with_noise.h”. Acknowledgements Thanks Jake for pointing me in the right direction, providing sample code for computing a complex number FFT. Assumptions Programming explanations and examples are for the C programming language. You understand what a FFT is used for.…