Dance Judge
How cool (or not cool) would you look busting moves to a certain song? Pick one, and let the Dance Judge be the… judge.
I first built the Dance Judge in 2017 as a small Node app that logged you in to Spotify and asked its Web API how danceable a song was. Spotify has since closed those audio-feature endpoints to hobby apps like this one, so this version does the listening itself.
When you pick a song, your browser downloads Apple’s 30-second preview and decodes it. The judge measures how much new sound arrives in each 12-millisecond slice, then looks for the delay at which that pattern best repeats: that’s the beat, and how cleanly it repeats is how strong the beat is. It also tallies the notes it hears against the 24 major and minor key profiles, and checks how loud, bright, and percussive the clip is.
A model fit to Spotify’s archived scores for 295 songs turns those measurements into Spotify’s old 0-to-1 scales. On songs it wasn’t fit to, the judge reaches the same verdict Spotify’s number would about three times in five, and comes within one verdict nearly every time. It only hears thirty seconds, though, and has opinions of its own. The verdicts are the same ones from 2017.