This is the real engine. The same measurements as the Python core — BS.1770 loudness, EBU R128 loudness range, 4× oversampled true peak, stereo phase, spectral tilt — ported to JavaScript. On the test fixtures its integrated loudness agrees with pyloudnorm, an independent BS.1770 implementation, to within 0.05 LUFS, and every score it shares with the Python core agrees to within 0.5 points. Those loudness and peak figures are measured against published standards; the genre profiles the scores are weighed against are declared starting points, not calibrated against a corpus of masters. Tempo, key and structure still need the server engine and are not shown here.