or click to choose — tempo and key are worked out in your browser, nothing is uploaded
Check the reading by ear: the click should sit on the beat, and the drone should sound like home.
Tempo autocorrelates a spectral-flux onset envelope — the beat period is the lag at which the whole track best repeats itself, reinforced at 2× and 4× the period and weighted toward ~120 BPM to settle half/double-time ambiguity. If it reads half or double what you feel, use × ½ / × 2. Key is Krumhansl–Schmuckler: fold every frequency onto its pitch class (the chromagram), then correlate against all 24 rotations of a major and a minor key profile. Relative major/minor pairs share their notes, so they're the usual close second — the runner-ups show how close. Mixing tip: keys one step apart on the Camelot wheel (the code next to the key) blend smoothly, as do relative major/minor pairs.