KeelrLeek
52f5878297
The prefix estimator is BIASED, not merely noisy, and the sign is known: a quiet opening under-reads the track, so the head asks for too much gain far more often than too little. Subtracting a constant moves the whole distribution toward the truth, so a first play begins nearer its real level and the correction that follows has less ground to cover. Measured by a new `head_start_offset_sweep` over 1046 tracks sampled across 182 artists — at most six per artist, spread across each discography rather than taken from the front, since openers are where intros are least typical and intros are the whole source of the bias. The cached corpus it replaces was a dozen artists and put the median at +3.48 dB. Sampled diversely it is +1.55, so the old number was overstating the bias by more than double. The size comes from the MARGINAL trade, not the smallest mean error: step loud fixed quiet created ratio 0.0 -> 0.5 -89 +41 2.2 : 1 0.5 -> 1.0 -83 +85 1.0 : 1 1.0 -> 1.5 -61 +132 0.5 : 1 Only the first step is clearly worth taking. mean|err| bottoms out at 1.5 dB instead and is the wrong objective: it weights an error that begins decaying at once the same as one that waits for Analysis::Complete, which on the streamed first plays this path exists for is download-bound and therefore late. A constant is deliberately a weak lever. The per-artist median error runs from -4.58 dB (Boards Of Canada) to +7.03 dB (Ponytail); no single number fits everyone, and an offset shifts that spread without narrowing it. The levers that would are letting the follow recover UPWARD, and predicting the offset per track from the prefix. Both still open. The overlay reports it as a MOVE — what the prefix asked for, where the track actually started, and a ghost tick on the dB scale at the prefix position, so the gap to the applied gain IS the head start. Gated on `analyzing`: at Analysis::Complete the player releases to the whole-track gain while loudness.gainDb goes on reporting the prefix value, which it keeps for the next play. Without that condition the line advertised a correction that had already been released.