Nerulio Audio Lab estimates BPM and major or minor key from a file you choose on your device. It can cut a waveform range, trim quiet edges, add fades, change playback speed and pitch separately, measure integrated LUFS, and save WAV, Ogg Vorbis or MP3. The estimates include confidence because a beat can be heard at half or double time and a song can change key. Editing and encoding happen inside this browser. iPhone M4R remains disabled until AAC in MP4 and phone playback have been verified.
How it works
The worker reads decoded samples locally. Spectral onset strength and autocorrelation estimate tempo; chroma and major/minor profiles estimate key. These are estimates, especially for speech, weak percussion or changing harmony.
A K-weighted, gated meter estimates integrated loudness. The displayed peak is the sample peak, not an oversampled true peak. A normalization target is limited by a −1 dBFS sample-peak ceiling.
Worked example
For a 16 second test clip constructed with 120 BPM clicks and C major chords, the analyzer reports a tempo near 120 BPM and C major while exposing half-time as another possible pulse. Choose a ten second range, fade both ends, preview the WAV, then save the selected format.
120 BPM × 16 s = 32 beatsCheck the result
- Check the displayed confidence and listen to the source against the beat and key estimate.
- Play the exported clip in another audio application and check the start, ending and fade for clicks.
- For loudness work, use an independent LUFS and true-peak meter before publishing.
Troubleshooting
| Symptom | Likely cause | How to check | Fix |
|---|---|---|---|
| Tempo is half or double | The rhythmic pulse is ambiguous | Compare the alternatives beneath BPM against the music | Use the value that matches counted beats |
| Key is unknown | The file is short, percussive or lacks stable harmony | Listen for sustained chords and review confidence | Use a longer harmonic passage |
| File cannot open | The browser cannot decode this codec or the file exceeds a local limit | Check duration, channels, size and the error in the status panel | Try a WAV or MP3 under three minutes |
Other ways to do it
| Option | When it is the better choice |
|---|---|
| A digital audio workstation | Use one when you need multitrack editing, manual note detection or mastering with true-peak metering |
What this page does not cover
- Maximum three minutes, stereo and 128 MiB input; some devices may have less usable memory.
- Pitch and time stretching can introduce audible artifacts, particularly at large shifts.
- M4R export and actual phone ringtone installation are unverified and disabled.
How to use Audio Lab
- Choose a local audio file. The waveform appears after browser decoding.
- Analyze BPM and key; check the confidence and half/double tempo suggestions.
- Set the start and end, audition changes, then choose a verified format and save.
How the measurements work
BPM uses spectral onset strength and a tempo autocorrelation. Key compares a 12-note chroma summary with major and minor profiles. Integrated loudness uses K-weighting and EBU R128 gates; a short or silent file may have no valid LUFS reading.
Limits and checks
Pitch and speed processing can make artifacts, especially at extreme settings. Listen to the download in another player. MP3 and Ogg are lossy; WAV is best when you plan to edit again. Ringtone installation differs by device.
Common questions
Is my file uploaded?
No. Decoding, analysis and encoding happen in this browser. A local file is not put in the URL.
Why might the BPM or key be wrong?
A half-time beat, a sparse rhythm, speech, an atonal section or a key change can confuse an estimator. Low-confidence results remain labelled as estimates.
Can I make an iPhone ringtone?
The 30-second safe preset and M4R output require verified AAC-in-MP4 and real iPhone import/play testing. M4R is currently unavailable.
Methods and sources
EBU R 128 · ITU-R BS.1770-5 · Apple GarageBand ringtone limit · WebCodecs codec support