docs: add README

README.md

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+# unisonus-livekit
+
+WebRTC audio infrastructure for **Unisonus** — a choir/music streaming application. Provides a LiveKit server and a custom choir audio mixer agent that subscribes to participant audio streams, mixes them, and publishes the combined output back to the room.
+
+## Architecture
+
+```
+Participants (up to 6)
+        │  audio tracks
+        ▼
+  choir-mixer agent
+  ├── subscribes to all participant audio
+  ├── normalises RMS per stream (target: -20 dBFS)
+  ├── noise-gates signals below -40 dBFS
+  ├── sums all streams
+  ├── soft-limits via tanh (no hard clipping)
+  └── publishes mixed audio track back to room
+        │
+        ▼
+  All room participants receive the mix
+```
+
+## Services
+
+| Service | Image | Ports | Description |
+|---------|-------|-------|-------------|
+| `livekit` | `livekit/livekit-server:latest` | `7880` (HTTP/WS), `7881` (RTC TCP), `50000-50100/udp` | LiveKit WebRTC media server |
+| `choir-mixer` | Built from `./choir-mixer/Dockerfile` | — | Python agent: subscribes, mixes, publishes |
+
+## Audio Mixer Details
+
+**File:** `choir-mixer/main.py` + `choir-mixer/mixer.py`
+
+| Parameter | Value |
+|-----------|-------|
+| Sample rate | 48 kHz |
+| Channels | Mono (1) |
+| Frame duration | 20 ms (960 samples/frame) |
+| Max simultaneous streams | 6 |
+| Target loudness | -20 dBFS (RMS) |
+| Noise gate | -40 dBFS (silence below this threshold) |
+| Limiter | tanh soft-limit (smooth saturation, no hard clipping) |
+| Stale frame timeout | 60 ms (frames older than this are discarded from mix) |
+
+The mixer runs at ~50 Hz (every 20 ms). Each cycle it:
+1. Collects the most recent frame from each active participant (discarding stale frames)
+2. Normalises each stream to -20 dBFS
+3. Noise-gates signals below -40 dBFS (suppresses background noise and keyboard clicks)
+4. Sums all streams into one
+5. Applies tanh soft limiting to prevent clipping
+6. Publishes the result as a mono 48kHz audio track
+
+## LiveKit Server Config
+
+**File:** `livekit.yaml`
+
+| Setting | Value |
+|---------|-------|
+| HTTP/WS port | 7880 |
+| RTC TCP port | 7881 |
+| RTC UDP range | 50000–50100 |
+| Node IP | 192.168.0.241 |
+| External IP | Disabled (LAN only) |
+| Room empty timeout | 300 s |
+| Max participants | 50 |
+| Log level | info |
+
+## Environment Variables
+
+| Variable | Required | Description |
+|----------|----------|-------------|
+| `LIVEKIT_API_KEY` | Yes | LiveKit API key (from `livekit.yaml` `keys:`) |
+| `LIVEKIT_API_SECRET` | Yes | LiveKit API secret |
+
+Copy `.env.example` to `.env` and fill in the values. The API key/secret pair must match what is configured in `livekit.yaml`.
+
+## Running
+
+```bash
+docker compose up -d
+```
+
+To check mixer logs:
+```bash
+docker compose logs -f choir-mixer
+```
+
+## Dependencies
+
+**Python** (choir-mixer):
+- `livekit` — LiveKit Agents SDK
+- `livekit-rtc` — RTC bindings
+- `numpy` — audio processing
+
+## Deployment
+
+Runs on `192.168.0.241` (albert-MacBookPro Linux server).
+
+| Endpoint | URL |
+|----------|-----|
+| LiveKit signaling | `ws://192.168.0.241:7880` |
+| LiveKit RTC TCP | `192.168.0.241:7881` |
+| LiveKit RTC UDP | `192.168.0.241:50000-50100` |