Day 15: Pitch detection
In a previous life I spent most of my time (free and otherwise) thinking about phonetics and the analysis of speech sounds. Like most scientific research, it was slow and tedious and oddly rewarding.
Back then I was already in a steady drift towards spending more time playing with computers than with my research, so a lot of my efforts went into studying Praat, a piece of software you've almost certainly never heard of, but that has probably been used in most of the phonetics research you've also never heard of.