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ADR-v2-098 — Beam-Steered Spatial VAD (2-mic direction-of-arrival gate)

Status: Accepted (2026-07-02) · Wave L Context links: cocktail (identity gate), denoise (spectral), audioguard (event), [[adr-011]]

Context

Wave L research (#3) — Cocktail Filter gates by speaker-embedding identity (needs enrollment, unreliable on <0.5 s windows per our live-testing memo); Noise Suppression and the Ambient Audio-Event Guard are spectral/event-based. A spatial (geometric) gate — estimate the sound's direction of arrival from a 2-mic array and drop anything not from the user's seat — is orthogonal, enrollment-free, cheap, and reverberation-robust, and it composes with Cocktail Filter as an independent second gate. Anchor: Knapp & Carter GCC-PHAT (classic TDOA); real-time on-device DoA (PMC8136617) — GCC-PHAT runs real-time on built-in mics.

Decision

Add an opt-in Beam-Steered Spatial VAD: [spatialvad] enabled=false, target_angle=0.0, tolerance_deg=35.0, mic_distance_m=0.14. Pure cores in spatialvad/beam.py: gcc_phat(sig_l, sig_r, fs, max_tau) → the inter-mic time delay via a phase-transform FFT cross-correlation (pure numpy, no model), tdoa_to_angle(tau, mic_dist_m) → the arrival angle, and spatial_gate(angle, target_angle, tol) → keep/drop. Stereo capture is the only extra. OFF by default.

Consequences

  • Enrollment-free geometric rejection of off-axis interferers (TV, colleague, passer-by).
  • Pure numpy FFT → fully testable with synthetic delayed signals; composes with Cocktail Filter.
  • Privacy (ADR-011): local audio only; nothing stored or sent.
  • Caveat: needs a 2-mic/stereo source and a rough mic spacing; a single built-in mic can't use it; off by default.