BPM & Key Finder: Song Tempo and Key Online
Read a track's tempo and musical key in your browser. Beat-accurate BPM from a small on-device model, key from classical chroma analysis.
Two questions, two different answers under the hood. Tempo comes from a compact beat-tracking model (Beat This!, ISMIR 2024) that reads a mel spectrogram of the clip and marks every beat; the BPM you see is measured from the actual beat times, not from a lookup table, so half-time and syncopated material lands where a musician would count it. Key comes from no model at all: a chromagram folds the spectrum into the twelve pitch classes, and the profile is correlated against the classic Krumhansl-Schmuckler major and minor templates. When nothing tonal stands out, drum loops, speech, the tool says so instead of guessing. The report shows both results with a confidence for the key, and downloads as JSON with the first beat times included.
How to Use It
- Upload your audio file and wait for the local preview to load.
- Adjust the settings: Choose whether to report tempo and key together or one of them alone, then run the analysis; the audio is examined the same way either way.
- Download the result: Download the processed file directly to your device.
Controls and Options
Tempo + key covers most uses. Switch to BPM only when tagging a DJ library where key comes from elsewhere, or Key only when checking what to transpose a backing track to. Low key confidence means the material is weakly tonal. Trust the no-clear-key verdict over a forced label.
Formats and Output
Reads common audio formats your browser can decode, including MP3, WAV, M4A, OGG, and FLAC, and exports the analysis as a small JSON report with BPM, beat count, first beat times, key, and confidence.
Frequently Asked Questions
How accurate is the BPM reading?
The beat tracker is parity-locked against its research reference: on the validation clips the shipped engine lands within a few hundredths of a BPM of the reference implementation, and the count comes from real detected beats rather than autocorrelation guesses.
What does the key confidence mean?
It is the margin between the best-matching key profile and the runner-up. Above roughly 0.3 the key is clear; near the 0.15 floor the tonality is weak, and below it the tool reports no clear tonal center instead of naming a key.
Why does my drum loop get no key?
Percussion spreads energy across all twelve pitch classes, so no key profile stands out. That is the honest answer for atonal material, a key label there would be noise.
Does it handle half-time or double-time feels?
The model marks beats where the rhythmic emphasis actually falls, so a half-time groove reads at its felt tempo. If you disagree with the octave, doubling or halving the reported BPM is always the alternative reading.
How long a clip can I analyze?
Up to ten minutes of audio is analyzed in one pass; longer files are truncated to the first ten minutes and the report says so. Thirty seconds of steady material is usually enough for a stable reading.
Is my audio uploaded anywhere?
Supported media processing runs on your device and file contents are not uploaded for processing. Site analytics and the assistant are separate.