Simple real FFT using Mac OS X Accelerate
create a command line tool, for eexample called "AccelerateTool". click on the blue Xcode porject icon (the name of project, eg "AccelerateTool") and then add the Accelerate framework:
Go into Build Phases Link Binary with Libraries choose Acclerate
the example wraps the code form Apple's documentation https://developer.apple.com/library/mac/documentation/Performance/Conceptual/vDSP_Programming_Guide/UsingFourierTransforms/UsingFourierTransforms.html#//apple_ref/doc/uid/TP40005147-CH202-SW1
to do the FFT and return magnitude