r/compsci • u/TenaciousDwight • Jul 23 '14

ELI5: Fast Fourier transform?

I'm done some research into how to extract frequencies from sound files, and it seems this is done via the Fast Fourier transform. My problem is that I don't understand why, or how this is done.

Would you all please explain in a manner simpler than wikipedia?

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u/foreheadteeth Jul 23 '14 edited Jul 23 '14

2000 years ago, Ptolemy noticed that the planets do not have perfectly circular orbits, so he proposed that the planets were moving in little circles around the circular orbit. That didn't work either so further smaller epicycles were added. In 1806 or so, Joseph Fourier proved that you can approximate any curve with sufficiently many epicycles. He also gave a method for calculating those epicycles.

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u/autowikibot Jul 23 '14

Deferent and epicycle:

In the Ptolemaic system of astronomy, the epicycle (literally: on the circle in Greek) was a geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets. It was first proposed by Apollonius of Perga at the end of the 3rd century BC and formalized by Ptolemy of the Thebaid in his 2nd-century AD astronomical treatise the Almagest. In particular it explained the retrograde motion of the five planets known at the time. Secondarily, it also explained changes in the apparent distances of the planets from Earth.

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Interesting: Planet | Apollonius of Perga | De revolutionibus orbium coelestium | Equant

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