Audio BPM & Key Detector
The BPM & Key Detector tool analyzes any audio file and extracts its approximate tempo in BPM and its musical key (like C major or A minor), using spectral analysis and pitch-class fingerprinting — without uploading the file to any server. Useful for music producers and video editors who need to match a track's speed or key before mixing it with other clips. Analysis is based on the opening minute of the file, which is enough for most tracks with a steady tempo and key.
Your audio file is processed on your device and is never uploaded to our servers.
Only use this tool with files you own or have the right to process.
This tool analyzes any audio file's tempo (BPM) and musical key entirely inside your browser — useful for producers and video editors who need to match a track's speed or key before mixing it with other clips. Analysis is based on the opening minute of the file, which is enough for most tracks with a steady tempo and key.
Tempo and key detection here uses approximate algorithms (spectral analysis and statistical correlation), not full music-theory analysis — the result may differ slightly from the actual tempo or key, especially for complex or tempo-changing tracks.
Drag an audio file here or choose one
MP3, WAV, M4A, or OGG
What this tool does
Analyses an audio file and estimates its tempo in beats per minute and its musical key, with a confidence indicator for each.
When to use it
- Matching music clips to mix together and needing their tempos.
- Finding a song's key to play or sing along to it.
- Organising a music library by tempo or key.
- Choosing background music that fits another clip rhythmically.
How to use it
- Put an audio file on the drop area or choose it.
- Run the analysis and wait for the result.
- Read the tempo, the key and the confidence level for each.
A practical example
Input
A music clip with a clear beat and tonal instruments.
Output
A readout giving the tempo in beats per minute and the key as major or minor, with a high, medium or low confidence level.
Limitations
- The maximum duration is 30 minutes.
- The confidence indicator is part of the result, not decoration: a low-confidence reading is a guess rather than a reliable answer.
- Clips with no clear beat or no tonal content produce an explicit message saying detection is not possible, rather than an arbitrary number.
- The tempo can come out at double or half the true value, a well-known ambiguity in every tempo-detection algorithm.
- The key is a statistical estimate and can be wrong on pieces that modulate between keys.
Privacy and processing
The analysis runs entirely inside your browser and the audio file is never uploaded.
Technical notes
- Tempo detection uses spectral-flux onset detection followed by autocorrelation to find the beat period.
- Key detection builds a twelve-bin pitch-class histogram and correlates it against the standard Krumhansl-Kessler major and minor key profiles.
- Both algorithms are written inside this project rather than imported, because the available libraries for this purpose carry copyleft licences incompatible with the project's dependency policy.
Frequently Asked Questions
No — all analysis happens directly in your browser; your file is never uploaded to a server.