// analyze · tool 13
BPM & Key Finder
Drop a song, get its tempo and musical key with confidence scores. Pure analysis — fast, shareable, nothing to download.
Drop your song here
MP3, WAV, M4A, OGG, FLAC and more — or click to browse
[ drop works anywhere on this page ]
How the analysis works
Everything runs in your browser, on up to 60 seconds from the middle of the track (the most rhythmically stable part). Tempo: the audio is reduced to an onset-strength envelope — a measure of "how much new sound just happened" — and autocorrelated; the lag with the strongest self-similarity is your BPM. Key: a Fourier transform folds the spectrum into a 12-bin chromagram (energy per pitch class), which is correlated against the Krumhansl-Schmuckler major and minor profiles in all 12 rotations; the best match wins, and the margin over the runner-up becomes the confidence score.
Who uses this
- DJs — match keys and tempos before mixing tracks (harmonic mixing).
- Producers — find a sample's key before pitching it into a project. Pair with our Pitch Shifter to transpose.
- Musicians — figure out what key to jam in over a backing track.
- Dancers & fitness instructors — confirm a song's BPM fits the routine.
FAQ
How accurate is the BPM detection?
For music with a steady beat — electronic, pop, hip-hop — typically within 1 BPM. Rubato material like solo piano has no fixed tempo, which the confidence score reflects.
Why does it sometimes show half or double the BPM?
Half/double-tempo ambiguity is inherent to beat detection. The analyzer prefers the 90–180 range; if the result feels wrong for the genre, halve or double it.
How is the key detected?
The spectrum is folded into a 12-bin chromagram and correlated against Krumhansl-Schmuckler major/minor profiles. The best rotation is the key; the margin to the runner-up sets the confidence.