Analysis guide · 6 min
Read an estimate like an engineer
Automatic analysis is a fast second opinion, not an authority. Use the main result, confidence, alternatives, and chroma together—and verify the decision against the music before changing a session or harmonic mix.
Quick start
A reliable starting point
- 01Choose a representative file
Use a clean, full-length export or a section with clear rhythm and harmony. Long silence and noisy intros weaken the evidence.
- 02Read beyond the headline
Compare confidence and alternatives. A close alternative is a signal to verify half/double tempo or a relative/parallel key.
- 03Confirm musically
Count against a metronome, align transients to a grid, and play the proposed tonic and scale over a stable section.
Privacy & processing
01Your audio stays in this browser
The selected file is decoded with Web Audio and analyzed in memory on your device. auroLab does not upload the file for BPM or key analysis.
Large or highly compressed files can take longer to decode. Browser codec support varies, so converting an unsupported source to WAV can be the most reliable fallback.
Tempo estimate
02From transients to BPM candidates
The analyzer resamples the mono signal to 44.1 kHz and runs Essentia's multifeature beat tracker. Five complementary rhythmic representations agree on beat positions and a tempo between 40 and 208 BPM. The final BPM is refined from the accumulated beat span, suppressing sub-BPM onset jitter between different mixes of the same production.
This approach works best when the rhythm produces clear onsets. Pads, rubato performances, extreme syncopation, and tracks with changing tempo may produce several plausible candidates.
- Half/double errors are normal: 75 and 150 BPM can explain related accent patterns.
- Alternatives are useful evidence, not failed answers. Test them against bar lines in the DAW.
- Low confidence means the leading candidate did not separate clearly from the next choices.
Key estimate
03Chroma, tonal profiles, and Camelot
Essentia first measures the track's tuning, then builds a 36-bin harmonic pitch-class profile. Several profiles specialized for pop, electronic, and tonal music vote across the full track and three temporal sections.
The chroma chart shows evidence across the whole track, not a chord transcription. Camelot notation translates the detected key into a compact code commonly used to compare harmonically related tracks.
- Major and relative minor share many notes, so ambiguous songs can score closely in both.
- Modal, atonal, heavily detuned, or key-changing material may not fit a single major/minor label.
- A dominant bass note or long intro can bias the global chroma. Recheck a harmonically stable section when possible.
Decision quality
04What confidence does and does not mean
Confidence is the separation between the best internal score and competing scores. It is useful for comparing this analyzer’s candidates, but it is not a calibrated probability that the label is correct.
Treat a strong result as permission to verify quickly, not to skip verification. For mastering, DJ preparation, sample clearance, or musicological work, confirm with a DAW grid and an instrument or a second analysis method.
Keep in mind
Studio notes
Percussive sections help tempo; sustained, harmonically stable sections help key.
The runner-up often reveals half-time or a closely related tonal center.
If the proposed tonic clashes consistently, the label is not useful—whatever the score says.