This is the detector behind Sonyk’s DJ decks: an onset-strength autocorrelation with sub-frame refinement, folded into the 70–180 BPM octave, cross-checked against a second estimator, plus a downbeat search. It is accurate to well under 1 BPM on club records with a steady tempo; live drummers and tempo changes will read as the dominant tempo.
Inside Sonyk the same analysis builds a beat grid you can true by ear, so two decks drop on the 1 and stems stay locked. See the DJ decks.