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ADR-v2-096 — Earcon Feedback Language (non-speech eyes-free state cues)

Status: Accepted (2026-07-02) · Wave L Context links: [[project_readback_loop]] (speech feedback), confidence (visual), overlay (visual), [[adr-011]]

Context

Wave L research (#6) — Read-Back is speech (slow, verbose); Confidence Ink and the Voice-Activity Overlay are visual. A structured non-speech auditory feedback grammar — a rising two-note motif for "recording started", a muted buzz for "low confidence", a distinct chime for "command executed" — is faster, less intrusive, and works with no screen, a gap in the current set. Anchor: Brewster et al., An evaluation of earcons (ACM TOCHI 1993); Gaver, Auditory Icons (1986); Walker et al., Spearcons (Human Factors 2013) — structured non-speech audio conveys interface state faster than speech and improves eyes-free navigation.

Decision

Add an opt-in Earcon Feedback: [earcon] enabled=false. Pure cores in earcon/tones.py: ToneSpec(freq_hz, dur_ms, envelope), earcon_for(event, confidence=None) → a motif (list of ToneSpec; low confidence overrides to a buzz), and render_earcon(specs, fs) → a numpy waveform (sine synth + linear/buzz envelope). Numpy is already a core dependency; no heavy extra. OFF by default.

Consequences

  • Fast, unintrusive, screen-free state feedback; complements (precedes) Read-Back.
  • Fully pure (mapping + numpy synth) → 100% testable, zero new dependency.
  • Privacy (ADR-011): synthesized locally; nothing stored or sent.
  • Caveat: a fixed motif vocabulary (user-remappable is a later tier); off by default.