RMixer - JACK Audio Mixer

A low-latency audio mixer application for JACK with a terminal user interface. Written in Rust.

Features

• Configurable Ports: Define input and output ports in YAML format
• Real-time Level Meters: Visual dB level indicators with green/yellow/red zones
  • Green: < -12 dB
  • Yellow: -12 dB to 0 dB
  • Red: ≥ 0 dB (clipping)
• 5-Second Peak Hold: Visual peak indicators with decay
• Volume Control: -60 dB to +12 dB range with 0.5 dB steps
• Mute & Solo: Per-channel mute and additive solo (inputs only)
• Mono/Stereo Support: Channels can be mono (1 port) or stereo (2 ports)
• Volume Persistence: Volume levels are saved to config file on exit
• Manual Connections: Ports are exposed for manual connection via jack_connect, qjackctl, etc.

Requirements

Build Dependencies

# Debian/Ubuntu
sudo apt install build-essential libjack-jackd2-dev libclang-dev

# Fedora
sudo dnf install gcc jack-audio-connection-kit-devel clang-devel

# Arch
sudo pacman -S base-devel jack2 clang

# NixOS
# Dependencies are handled automatically via the Makefile

Runtime Dependencies

• JACK server (running via jackd, pipewire-jack, or similar)

Building

make build        # Debug build
make release      # Release build

Or directly with cargo (non-NixOS):

cargo build --release

Usage

rmixer --config config.yaml

Command Line Options

• -c, --config <PATH>: Path to configuration file (required)
• -v, --verbose: Enable verbose logging
• -h, --help: Print help
• -V, --version: Print version

Configuration

Configuration is done via a YAML file. See config.example.yaml for a full example.

# JACK client name
client_name: "Mixer"

# Input channels to mix
inputs:
  - name: "Mic"           # Display name
    ports:
      - "mic_in"          # Mono: single port

  - name: "Music"
    ports:
      - "music_in_L"      # Stereo: two ports
      - "music_in_R"

# Output channels (receive sum of all inputs)
outputs:
  - name: "Main"
    ports:
      - "main_out_L"
      - "main_out_R"

Ports are exposed as {client_name}:{port_name}, e.g., Mixer:mic_in.

Volume levels are automatically saved to the config file on exit and restored on next startup:

inputs:
  - name: "Mic"
    ports:
      - "mic_in"
    volume_db: -6.0       # Optional: saved volume level

Controls

Key	Action
← / →	Select channel
↑ / ↓	Adjust volume (±0.5 dB)
0	Reset volume to 0 dB
m	Toggle mute
s	Toggle solo (inputs only)
Tab	Switch between inputs/outputs
q / Esc	Quit

Connecting Ports

RMixer does not auto-connect ports. Use external tools to make connections:

# List available ports
jack_lsp

# Connect ports
jack_connect "Mixer:mic_in" "system:capture_1"
jack_connect "Mixer:main_out_L" "system:playback_1"
jack_connect "Mixer:main_out_R" "system:playback_2"

Or use graphical tools like qjackctl, qpwgraph, or helvum.

Architecture

┌─────────────────────┐         ┌─────────────────────┐
│    Audio Thread     │         │     UI Thread       │
│                     │         │                     │
│  JACK Process       │◄───────►│  ratatui + crossterm│
│  Callback           │  rtrb   │  Event handling     │
│  Level metering     │         │  Rendering          │
└─────────────────────┘         └─────────────────────┘

• Lock-free communication via rtrb ring buffers
• Real-time safe audio processing (no allocations in audio callback)
• Synchronized I/O: Single JACK process callback handles all inputs and outputs
• 60 FPS UI refresh rate

License

MIT