nx_aec.nx

nx_aec.nx -- R4a: sovereign Acoustic Echo Canceller. The reserved-but-empty nx_aec slot in nx_audio_session, now built. Adaptive FIR (NLMS) in INTEGER fixed-point (NO-FLOAT doctrine): it learns the echo path (speaker->room->mic) from the far-end reference and subtracts the predicted echo from the mic signal, so the far end doesn't hear itself. y[n] = (sum_k w[k]*x[n-k]) >> Qw (predicted echo from far-end reference x) e[n] = d[n] - y[n] (mic d minus predicted echo = the cleaned output) w[k] += mu * e[n] * x[n-k] / (||x||^2 + eps) (NLMS update, normalized step) MEASURED metric = ERLE (Echo Return Loss Enhancement) = echo power BEFORE / AFTER cancel. Negative controls: (T2) adaptation OFF -> e==d -> no cancellation (the filter is load-bearing); (T3) DOUBLE-TALK -- with the converged filter frozen, near-end speech must SURVIVE while the echo is removed (a broken AEC would crush the near-end too); (T4) ERLE improves over time (it LEARNS). main() is the SELF-VALIDATING GATE. Evidence -> knowledge/status/aec.log. license_tier: ORIGINAL