FFT's

Do I look like Google to you?

Think Liberally.

... or go to your local library and borrow just about any book on engineering mathematics (or spectral analysis).

Timkin

http://www.dspguide.com/pdfbook.htm

There is a fairly easy to understand article at http://www.relisoft.com/freeware/freq.html

What are you trying to do?

Author, "Real Time Rendering Tricks and Techniques in DirectX", "Focus on Curves and Surfaces"

Fun stuff, learning math about 6 years ahead of my geometry class.

I don''t want to be redundant on top of the great replies that the moderators offered but a good explanation of the FFT algorithm is in "Wavelets made easy" by Nievergelt. This book is not great for an all around undertanding of fourier transforms though. I took a class on FT and the book we used gave a more complete explanation of the method and what you want to use it for, "a first course in fourier analysis" by kammler. It''s not a great book(i think, though everyone seems to disagree with me), but its definetly thorough.

-Grady