Find the key, tempo and tuning of any track.

Reading the numbers

Key

The key is the note and scale a track centres on, written the way you would write it on a chart: A minor, B flat major. The relative key shown next to it shares exactly the same notes, which is why a track in A minor sits comfortably against one in C major. Strength says how clearly the track committed to a single key, on a scale from 0 to 1: the higher it is, the more you can trust the read. Drum loops, sound effects and heavily processed material often have no key to find, and the figure will wander.

Tempo

Tempo is counted in beats per minute. A first estimate appears within a second or two, then a slower pass refines it and reports how strongly the beats lined up. Press play to hear the track against the beat grid: if the marks land with the snare, the number is right. If the result is exactly half or double what you expected, the pulse is genuinely ambiguous and both readings are defensible.

Tuning

Tuning is the reference pitch the recording actually sits at, given as the frequency of the A above middle C and as a distance in cents from the 440 Hz standard. A cent is a hundredth of a semitone. Records made in the last thirty years sit at or very near 440. Older ones drift, sometimes by a quarter of a semitone, because tape machines and cutting lathes ran at slightly different speeds. If you are sampling and the result fights your own instruments, this is the number that tells you how far to pitch it.

Nothing is uploaded

The measuring is done by a WebAssembly build of Essentia, the audio analysis library from the Music Technology Group at Universitat Pompeu Fabra, running inside this page. Your file is read by the browser, measured, and forgotten when you close the tab. There is no account and no server-side copy. Once the page has loaded you can disconnect from the network and it will carry on working.

The site does count how it is used, through PostHog: page visits, how long each analysis took, and what it found (the key, tempo and tuning, but never the audio or the file's name). No cookies are set and nothing identifies you.

On the command line

There is a terminal version for doing a whole folder at once. It writes the key and tempo into each file's own tags, so Rekordbox, Serato and Traktor pick them up without you typing anything, and it can rename files to the bracketed form DJs use for sample folders.

git clone https://github.com/mikeyfarina/keyandbpm
cd keyandbpm && bun install
bun apps/cli/src/cli.ts --tag --rename ~/samples/*.mp3

Needs Bun and ffmpeg.