The Hidden Spectral Sector: Conservation, Spectral Missingness and Latent-State Inference in a Dynamical Audio System

A real-time spectral architecture in which the expected-minus-observed spectral residual (energy that should have arrived but did not) is deposited into a hidden sector of latent states and later re-emitted: absence becomes an event. Reports an exactly conserved spectral coefficient quantity C (amplitude-like, not acoustic energy) with a small conservation calculus across event transformations under four conservation-constrained event transformations, the absence-event demonstration (a removed harmonic re-emerges as a delayed latent resonance), and two design results (residual on the exogenous input model; a significance threshold for background rejection). Methodological transfer from missing-energy inference in experimental physics; no physical or dark-matter claim is made. Fourth note in the Harmonic DAW research series.