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:

Collects the most recent frame from each active participant (discarding stale frames)
Normalises each stream to -20 dBFS
Noise-gates signals below -40 dBFS (suppresses background noise and keyboard clicks)
Sums all streams into one
Applies tanh soft limiting to prevent clipping
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

docker compose up -d

To check mixer logs:

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`

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