Not too long ago, we finished an Arduino FFT library, which added frequency spectrum analysis to the list of things you can do with an Arduino. Now you can do that same task in half the time and half the memory usage, thanks to the Fast Hartley Transform (FHT). It’s identical to the FFT, except that it was designed specifically for processing real audio data, which is exactly what we’re all about here. It can do a 256 point spectrum in 3.2ms! That’s fast enough to be sampling at 40ksps and not miss a beat. And we bundled it up into a nice Arduino library with examples, so check it out:
This transform is named after the same Ralph Hartley that gave us the Hartley oscillator. So thanks to Ralph for coming up with this nice transform back in 1942, and to Ronald Bracewell for making the dicrete version in 1983, and finally to Stanislav for introducing it to me in 2012.