Function integratedLoudness

Gated INTEGRATED loudness (LKFS) — ITU-R BS.1770-5 Annex 1, eqs.3-7 (p.6-7).

Two-stage gate:

1. Absolute: keep blocks with l_j > Γ_a (-70 LKFS).
2. Relative: from the absolute-gated set, compute the mean loudness, set Γ_r = mean - 10 LU, then keep blocks with l_j > Γ_r (and still > Γ_a). The final loudness averages the per-channel mean-squares over the surviving block set, then applies the loudness formula (eq.5) — averaging in the power domain, NOT averaging the per-block LKFS values.

Returns -Infinity if no block survives (e.g. all-silent input).