Raspberry Pi Real-Time Audio Mixer
A professional multi-channel real-time audio mixer running on a Raspberry Pi 4B. Sub-10ms round-trip latency with 16-channel USB audio, MIDI controller support, touchscreen UI, multi-track recording, live streaming, and a web control surface.
Features
- 16-channel mixer with 3-band EQ, compressor, gate, gain, pan, mute, solo per channel
- 4 aux sends, 2 subgroups, 2 VCA groups, master bus with dim and monitor
- MIDI controller support — CC, NRPN, learn mode, clock sync, JACK MIDI bridge
- Multi-track recording — per-channel WAV capture with write-ahead buffering, punch in/out
- Backing track player — sync'd playback with metronome, loop/one-shot/segue modes
- Live streaming — GStreamer H.264 to YouTube, Twitch, Facebook, or custom RTMP
- Session manager — save/load mixer states, setlists with transitions, auto-save
- Touchscreen UI — Kivy-based multi-touch interface for 5"/7" displays
- Web control surface — FastAPI REST API + WebSocket real-time updates
- OSC server — Open Sound Control for DAW integration (Ableton, Reaper, etc.)
- Plugin host — LV2, VST2, NAM neural amp models via Carla rack
- Fader automation — record, playback, scenes with interpolation
- SD card image builder — automated build script produces ready-to-flash images
Architecture
┌──────────────────────────────────────────────────────────────┐
│ User Interfaces │
│ ┌─────────────┐ ┌──────────────┐ ┌────────────────────┐ │
│ │ Touch UI │ │ Web UI │ │ MIDI Controllers │ │
│ │ (Kivy/HDMI) │ │ (FastAPI) │ │ (USB/ALSA seq) │ │
│ └──────┬──────┘ └──────┬───────┘ └────────┬───────────┘ │
│ │ │ │ │
├─────────┼────────────────┼────────────────────┼──────────────┤
│ │ REST/WS │ OSC │ MIDI/CC/NRPN │
│ ┌──────▼────────────────▼────────────────────▼──────────┐ │
│ │ Mixer Engine (Python) │ │
│ │ ┌──────────┐ ┌──────────┐ ┌──────────┐ ┌──────────┐ │ │
│ │ │DSP Engine│ │Recording │ │ Streaming│ │ Session │ │ │
│ │ │+ Carla │ │(WAV) │ │(GStream) │ │ Manager │ │ │
│ │ └────┬─────┘ └──────────┘ └──────────┘ └──────────┘ │ │
│ │ │ OSC │ │
│ │ ┌────▼─────────────────────────────────────────────┐ │ │
│ │ │ Carla Rack (LV2/VST/NAM) │ │ │
│ │ └────────────────────┬─────────────────────────────┘ │ │
│ └───────────────────────┼────────────────────────────────┘ │
│ │ JACK │
│ ┌─────▼──────┐ │
│ │ JACK2 RT │ SCHED_FIFO prio 70 │
│ └─────┬──────┘ │
│ │ ALSA hw:USB │
├──────────────────────────┼────────────────────────────────────┤
│ Kernel │ │
│ ┌───────────────────────▼──────────────────────────────┐ │
│ │ PREEMPT_RT 6.12.y │ snd-usb-audio │ xHCI USB │ │
│ └──────────────────────────────────────────────────────┘ │
└──────────────────────────────────────────────────────────────┘
Quick Start
Option 1: Download SD Card Image (Recommended)
- Download the latest
rpi-audio-mixer-*.img.xzfrom Releases - Flash to a 16GB+ SD card:
xz -d rpi-audio-mixer-*.img.xz sudo dd if=rpi-audio-mixer-*.img of=/dev/sdX bs=4M status=progress conv=fsync - Insert SD card into RPi 4B, connect USB audio interface, power on
- Follow the first-boot setup wizard on HDMI display
- Open
http://pi-mixer.local:8080in your browser
Option 2: Build from Source
# Install build dependencies
sudo apt install wget xz-utils dosfstools e2fsprogs qemu-user-static
# Quick build (stock kernel, 10-15 min)
./build/build.sh --skip-kernel
# Full build with PREEMPT_RT kernel (30-45 min)
./build/build.sh
See docs/build-guide.md for detailed instructions.
Option 3: Development Setup
# Install dependencies
sudo apt install jackd2 carla python3-pip
pip install fastapi uvicorn python-jack-client numpy
# Run tests
python -m pytest tests/ -v
# Start the API server (without full hardware)
python -m src.network.run
Project Structure
├── src/
│ ├── mixer/ DSP engine, channel strips, routing, OSC, automation
│ ├── midi/ MIDI engine, learn mode, clock sync, device discovery
│ ├── session/ Session manager, setlists, snapshots
│ ├── recording/ Multi-track WAV recorder with punch in/out
│ ├── backing/ Backing track player, metronome, transport
│ ├── streaming/ GStreamer pipeline, platform presets, camera
│ ├── network/ REST API, WebSocket, OSC server, auth
│ ├── plugin/ Plugin manager, LV2/VST/NAM support, scanner
│ └── ui/ Kivy touchscreen UI, widgets, screens
├── tests/ 735 tests (pytest)
├── build/ SD card image builder + first-boot scripts
├── scripts/ Utility scripts (Carla presets, LV2 lint, NAM build)
└── docs/ User and developer documentation
Documentation
| Document | Description |
|---|---|
| docs/build-guide.md | Step-by-step SD card image build instructions |
| docs/user-manual.md | Comprehensive mixer operation guide |
| docs/hardware-compatibility.md | Tested USB interfaces, MIDI controllers, displays |
| docs/developer-guide.md | Architecture, contributing, source build |
| docs/troubleshooting.md | Common issues and solutions |
| build/README.md | Image builder reference |
System Requirements
- Computer: Raspberry Pi 4 Model B (4GB+ RAM recommended)
- SD Card: 16GB+ Class A2 (32GB+ recommended for recordings)
- Display: HDMI touchscreen (official 7" or Waveshare 5") or headless via web UI
- Audio: USB audio interface (class-compliant UAC2)
- Network: Ethernet recommended; WiFi supported
- Power: 5V/3A USB-C power supply
Performance
| Metric | Value |
|---|---|
| Round-trip latency | <10ms (128 frames @ 48kHz) |
| Channels | 16 mono / 8 stereo |
| Sample rate | 48 kHz (44.1k and 96k supported) |
| Bit depth | 32-bit float (internal), 16/24-bit WAV |
| CPU usage (idle) | ~5% (all 16 channels driven) |
| Recording tracks | Up to 16 simultaneous WAV |
| Streaming | 1080p30 H.264 @ 4-8 Mbps |
Status
All planned phases complete:
- P1: System Research & OS Selection — RPiOS Lite + PREEMPT_RT
- P2: ALSA + JACK2 Low-Latency Configuration
- P3: Core Mixer Engine, Backing Tracks, Multi-Track Recording
- P4: MIDI Controller Support with Learn Mode
- P5: Web App + Touchscreen UI (Kivy)
- P6: Streaming Pipeline + Session Manager
- P7: SD Card Image Builder + Documentation
License
MIT