FFT class or routines

I want to do an FFT analysis of audio data in a professional music production app. I've been trying to use a class called RealFFT, but I don't have the technical knowhow to peice the audio back together after the IFFT. I was wondering if there is some Delphi code of some component out there which will make it easy to get the frequency info and then convert that back into PCM.
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