If you use a filter with the same shape as the sweep filter on the magnitude values from the FFT, and the FFT was done with a sensible windowing function, the results should match for truly periodic signals.

that's a lot of "if"s there

> ... I don't know my arse from my elbow when it comes to electrical engineering and all that so I have a couple of questions. 1. Do I need to have a background in engineering to use an Arduino. ... [from this post]