Here's an FFT implementation I used many years ago to implement a spectrum analyzer in a music recorder. It worked great back then, should work even better now!

Found the original at: https://www.musicdsp.org/en/latest/Analysis/ in FFT section:

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A paper (postscript) and some C++ source for 4 different fft algorithms, compiled by Toth Laszlo from the Hungarian Academy of Sciences Research Group on Artificial Intelligence. Toth says: "I've found that Sorensen's split-radix algorithm was the fastest, so I use this since then (this means that you may as well delete the other routines in my source - if you believe my results)."

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So I put those 150 lines directly into my recorder and forgot the rest. This is the code I mentioned at NDC TechTown 2021 in my talk about 'Real Programming'. Included in a separate file for easy access.

I just love the original coding style, the haphazard formatting, the lack of comments, it's everything that good code should be - fast, consice and without formal crap. Also not really seaplusplus, this is plain old C the way we like it.

Sjur Julin