Mastering louder does not make you louder.

Every platform measures the integrated loudness of what you deliver and applies one gain to reach its own target. That gain is one subtraction — target minus your loudness — and it undoes, exactly and completely, whatever you did to make the file loud. A master at -6 LUFS is turned down 8 dB to reach Spotify's -14 and plays back at exactly the same loudness as a master at -14 that was turned down by nothing at all. The two differ in one respect: the loud one has 8 dB less room to move.

The engine is free and needs no account. Paste what your meter says and every destination's gain comes back — and the same gain applied to the true peak, which is where the interesting failure lives. A platform that raises a quiet delivery raises its peaks too, so a file that measured legal in the studio arrives clipped, and no meter in the room could have shown it because the distortion does not exist until after delivery. It also separates a peak that was already over from one the platform pushed over, a broadcast spec that rejects from a streaming target that normalises, and track normalisation from album normalisation — which are two different records from the same set of numbers. Every lane ships a worked example that costs nothing. Writing the report needs credits.