JACK Ports → MixerEngine::process() → JACK Ports
                  ↕
         MixerControlServer (Unix socket)
                  ↕
         FastAPI bridge (future) / socat / nc
                  ↕
         React Mixer Console (browser)

Processing Pipeline (per audio cycle)

Clear all bus buffers
For each channel: apply HPF → volume/pan → accumulate to routed buses
Process aux sends (pre/post fader)
Route buses to buses according to routing matrix
Process each bus (apply volume, compute VU)
Write to physical outputs per output routing table

Dependencies

JACK (libjack-jackd2-dev on Debian, jack-audio-connection-kit-devel on Fedora)
CMake >= 3.16
C++17 compiler
nlohmann/json (auto-fetched by CMake)

Build

git clone <repo-url> oplabs-mixer-daemon
cd oplabs-mixer-daemon
mkdir build && cd build
cmake ..
make -j$(nproc)

Run

# Start JACK first
jackd -d alsa -r 48000 -p 256 -n 3 &

# Run the daemon (auto-connects to JACK)
./mixer-daemon

# With custom config
./mixer-daemon --inputs 4 --outputs 2 --buffer-size 128

Command-line Options

Option	Default	Description
`--socket <path>`	`/tmp/mixer-daemon.sock`	Unix socket path
`--inputs <N>`	2	Number of JACK input channels
`--outputs <N>`	2	Number of JACK output channels
`--sample-rate <N>`	48000	Audio sample rate (overridden by JACK)
`--buffer-size <N>`	256	Audio buffer size in frames (overridden by JACK)
`--help`		Show help

Headless Mode

If JACK is not running, the daemon starts in headless mode — no audio I/O, but the control socket is active for testing.

Control Protocol

The daemon listens on a Unix domain socket. Send one JSON command per line, receive one JSON response per line.

# Get full mixer state
echo '{"cmd":"getState"}' | nc -U /tmp/mixer-daemon.sock

# Set channel volume
echo '{"cmd":"setChannelVolume","channel":0,"volume":-6.0}' | nc -U /tmp/mixer-daemon.sock

# Get VU levels
echo '{"cmd":"getVU"}' | nc -U /tmp/mixer-daemon.sock

# Auto-create channels
echo '{"cmd":"autoCreateChannels","inputs":4,"outputs":2}' | nc -U /tmp/mixer-daemon.sock

Commands

Command	Parameters	Description
`getState`	—	Full mixer state as JSON
`getVU`	—	VU levels per channel and bus
`setChannelVolume`	`channel`, `volume`	Set channel fader (-96..+12 dB)
`setChannelPan`	`channel`, `pan`	Set pan (-1.0 left to 1.0 right)
`setChannelMute`	`channel`, `mute`	Mute toggle
`setChannelSolo`	`channel`, `solo`	Solo toggle
`setChannelLabel`	`channel`, `label`	Set channel name
`setBusVolume`	`busId`, `volume`	Set bus fader (-96..+12 dB)
`setBusMute`	`busId`, `mute`	Bus mute toggle
`routeChannelToBus`	`channel`, `busId`, `level`	Route channel to bus
`routeBusToBus`	`sourceBusId`, `targetBusId`, `level`	Route bus to bus
`removeRoute`	`sourceId`, `targetBusId`	Remove a route
`autoCreateChannels`	`inputs`, `outputs`	Recreate all channels for N inputs
`addChannel`	`physicalInput`	Add a new channel strip
`removeChannel`	`channel`	Remove a channel strip

Run Tests

cd build && ctest
# or
./mixer-test

Integration

The daemon is designed to sit behind a FastAPI Python bridge that translates HTTP/WebSocket to Unix socket commands. That bridge then serves the React Mixer Console UI.

README.md

OPLabs Mixer Engine — Standalone Daemon

Architecture