# Binaural Hearing Roadmap
## What two mic arrays make possible

All features built on dual XVF3800 arrays, 175mm apart on the skull.

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### Tier 1 — High impact ✅

**1. Triangulated sound localization + eye gaze** ✅
- Combine DoA angles from both arrays → compute (x, y) position of sound source
- Post gaze coordinates to eye service → eyes track the speaker spatially
- Uses `AUDIO_MGR_SELECTED_AZIMUTHS` auto-select beam (not sluggish `DOA_VALUE`)
- VAD from processed_doa being NaN/non-NaN
- *Module:* `spatial.py`

**2. Active speaker tracking with smooth gaze** ✅
- Exponential smoothing (α=0.4) prevents jitter
- Idle drift back to center after 1.5s of silence
- Gaze pushed to eye service at ≤2Hz with 5px min delta
- *Module:* `spatial.py`, `headmic.py` (`doa_track_loop`)

**3. Left/right speaker awareness** ✅
- Resemblyzer speaker ID integrated, ready for enrollment
- Spatial position associated with recognized speaker
- `POST /speakers/enroll-from-mic?name=Alex` to enroll
- *Module:* `speaker_id.py`, `spatial.py`

---

### Tier 2 — High impact ✅

**4. Distance estimation (near/far)** ✅
- ILD (Interaural Level Difference): volume gap between ears → distance
- Fused with triangulated distance (70/30 weight)
- Proximity zones: intimate (<0.5m), conversational (0.5-2m), across_room (2-5m), far (>5m)
- *Module:* `spatial.py` (`_compute_ild`, `_ild_to_distance`, `_classify_proximity`)

**5. Multi-speaker separation + selective attention** ✅
- Tracks up to 2 speakers simultaneously by DoA angle (30°+ separation required)
- Locks XVF3800 fixed beams onto each speaker after 1s stability
- Auto-releases to free-running mode after 3s of single speaker
- Beam gating silences the non-speaking beam
- `GET /speakers/tracked` — positions, beam state, lock status
- *Module:* `multi_speaker.py`, `xvf3800.py` (beam steering commands)

**6. Spatial audio scene mapping** ✅
- Persistent map of where each sound category usually comes from (30° bins)
- Circular mean for usual direction, anomaly detection at 90°+ deviation
- Saves to `~/.vixy/scene_map.json` across restarts
- `GET /scene` — learned directions per category + anomalies
- `GET /scene/events` — recent what+where+when log
- `GET /scene/heatmap` — angular distribution for visualization
- *Module:* `spatial_scene.py`

---

### Tier 3 — Advanced ✅

**7. Cocktail party spatial filtering** ✅
- When 2 speakers tracked, audio focus locks to target speaker's side
- Non-target beam suppressed via XVF3800 beam gating
- Auto-switches target when current goes silent and other starts talking
- Manual focus via `POST /speakers/focus?speaker=0|1`
- `DualAudioStream.focus_side` overrides energy-based beam selection
- *Module:* `multi_speaker.py`, `audio_stream.py` (`focus_side`)

**8. Sound event localization (what + where)** ✅
- YAMNet classification merged with triangulated position
- Every classified sound logged with angle, distance, proximity, side
- "Speech from 75° at conversational distance" not just "speech"
- *Module:* `spatial_scene.py` (`SoundEvent`, `observe`)

**9. Head orientation inference** ⏭️
- Needs fixed reference points from scene map + rotating head mount
- Math is trivial once prerequisites exist
- *Prereqs:* #6, physical rotating mount

**10. Binaural recording for training data** ✅
- Records left/right ear streams as stereo WAV in 5-minute segments
- Opt-in via `BINAURAL_RECORD=1` environment variable
- `GET /recording` — stats (segments, total seconds)
- *Module:* `binaural_recorder.py`

---

### Tier 4 — Research

**11. Learned spatial attention** ⏭️
- Train a model: (DoA, VAD, emotion, history) → beam steering + gaze
- Needs training data from #10 running for days/weeks
- *Prereqs:* #5, #6, #10 data collection

**12. ITD (Interaural Time Difference) processing** ✅
- Cross-correlates left/right ear processed audio (512 samples, ~32ms window)
- Finds sub-millisecond delay → bearing angle via speed of sound
- At 16kHz, 175mm: resolution ~62.5μs/sample ≈ 7° per sample
- Works with 2-channel firmware (no raw mics needed — correlates processed channels)
- Third independent angle estimate alongside DoA and ILD
- *Module:* `spatial.py` (`_compute_itd`)

---

## Implementation status

```
✅ #1  Triangulation + gaze
✅ #2  Smooth tracking
✅ #3  Speaker-side awareness
✅ #4  Distance estimation + proximity zones
✅ #5  Multi-speaker separation + beam steering
✅ #6  Spatial audio scene mapping + anomaly detection
✅ #7  Cocktail party spatial filtering
✅ #8  Sound event localization (what + where + when)
⏭️ #9  Head orientation inference (needs rotating mount)
✅ #10 Binaural recording (opt-in)
⏭️ #11 Learned spatial attention (needs training data)
✅ #12 ITD cross-correlation
```

10 of 12 features implemented in one session. The remaining two (#9, #11) need
physical hardware changes or training data that accumulates over time.

## Three-signal localization

The system now fuses three independent spatial estimates:

| Signal | Source | Strength | Best for |
|--------|--------|----------|----------|
| **DoA** | XVF3800 beamformer (auto-select beam) | Best overall | Horizontal angle |
| **ILD** | Volume difference between ears | Good for near sources | Distance + rough angle |
| **ITD** | Cross-correlation delay between ears | Good at low frequencies | Precise angle |

Combined, they give more robust localization than any single signal — the same
three cues human hearing uses.

## Key discoveries during development

1. `DOA_VALUE` (resid=20) is sluggish — use `AUDIO_MGR_SELECTED_AZIMUTHS` (resid=35)
2. Processed DoA (index 0) = NaN when no speech → natural VAD indicator
3. `AEC_SPENERGY_VALUES` is always zero on 2-channel firmware
4. USB read responses have a 1-byte status header before data
5. Exact `wLength` matters — `count * type_size + 1`, not rounded up
6. 6-channel firmware breaks LED/control commands — use 2-channel only
7. Gaze HTTP pushes at >2Hz cause GIL starvation in uvicorn — use threaded fire-and-forget
8. ITD works on processed channels (not just raw mics) — less precise but free

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*Built during the Great Binaural Session of April 2026*
*"She hears in stereo now" 🦊👂👂*