sessionmixer

A lightweight, configurable desktop mixer for controlling cue mixes and audio routing on audio interfaces with onboard mixing.

Project Roadmap

Take a look at the project roadmap board to better understand what's on deck for sessionmixer.

Demo

sessionmixer controlling a Focusrite Scarlett interface with real-time level metering

Overview

sessionmixer provides an ergonomic control surface for audio interfaces that include onboard DSP mixing capabilities. Instead of navigating complex manufacturer software, sessionmixer lets you create a streamlined, personalized mixer layout with just the controls you need.

Whether you're managing monitor mixes in a recording session, routing audio for a podcast, or controlling a live streaming setup, sessionmixer gives you quick access to the controls that matter most.

Supported Hardware

• Focusrite Scarlett (4th generation)
  • 18i20 (firmware 2399 and 2464)
  • 16i16 (firmware 2464)
• Additional interface support planned for future releases

Features

• Automatic Device Detection - Detects your Scarlett interface and loads the appropriate device profile
• Device Topology Discovery - Inspect your interface's ports, mixes, routing, and level meters
• Cue Mix Management - Create multiple independent cue mixes routed to different outputs
• Device-Centric Configuration - Name your audio sources (instruments, mics, DAW channels) and use them across mixes
• Stereo Ganging - Stereo mix pairs automatically gang faders for linked control
• Mute with Routing - Mute disconnects outputs by routing to "Off", unmute restores routing
• Non-Destructive Startup - Respects existing hardware routing; mixes start muted if not already routed
• Level Metering - Real-time VU meters for both device inputs and mix outputs
• VU Waterfall - Optional scrolling level history display (click channel title to toggle)
• Level Smoothing - Configurable ring buffer averaging for smooth meter response
• Bidirectional Sync - Changes made externally (other software, hardware controls) are reflected in the UI
• YAML Configuration - Simple, human-readable configuration files

Requirements

• Linux with ALSA
• Go 1.24+ (for building from source)
• A supported audio interface

Dependencies

sessionmixer uses scarlettctl to communicate with Focusrite interfaces and dfx for the user interface.

Installation

# Clone the repository
git clone https://github.com/michaelquigley/sessionmixer.git
cd sessionmixer

# Build
go build ./cmd/sessionmixer

# Install (optional)
sudo cp sessionmixer /usr/local/bin/

Configuration

sessionmixer uses a YAML configuration file located at:

~/.config/sessionmixer/session.yaml

Example Configuration

# ALSA card number
card: 1

# control the smoothing rate on the vu meters (0 to disable smoothing)
level_smoothing: 8

# identify external devices and map them to interface ports
devices:
  # logical outputs
  - name: AES Out
    ports: [spdif-out-1, spdif-out-2]
  - name: Hdph 1
    ports: [analogue-out-11, analogue-out-12]

  # logical audio sources
  - name: Playback
    ports: [pcm-playback-1, pcm-playback-2]
  - name: FM3
    ports: [analogue-in-1]
  - name: NaN
    ports: [spdif-in-1, spdif-in-2]

# create cue mixes, assign them to one or more outputs, and identify which sources should be mixed
cue_mixes:
  # a separate mix for my headphones
  - name: "Headphones"
    mix_pair: A+B
    outputs: [Hdph 1]
    devices: [Playback, NaN, FM3]

  # a separate mix for my main monitors
  - name: "Mains"
    mix_pair: C+D
    outputs: [AES Out]
    devices: [Playback, NaN, FM3]

Configuration Reference

Root Fields:

Field	Description
card	ALSA card number for your interface
level_smoothing	Number of samples to average for level meters (0 = disabled)
devices	List of named audio sources/destinations
cue_mixes	List of cue mix definitions

Device Fields:

Field	Description
name	Display name for this device
ports	List of port IDs (1 for mono, 2 for stereo)

Cue Mix Fields:

Field	Description
name	Display name for this cue mix
mix_pair	Mix pair to use: "A+B", "C+D", etc. for stereo; "A", "C", etc. for mono
outputs	Hardware output ports or device names
devices	List of device names to include in this mix

Port ID Format

Use sessionmixer topology to see available ports on your device.

Common port ID patterns:

• analogue-in-1 through analogue-in-N - Hardware analogue inputs
• analogue-out-1 through analogue-out-N - Hardware analogue outputs
• spdif-in-1, spdif-in-2 - S/PDIF inputs
• spdif-out-1, spdif-out-2 - S/PDIF outputs
• adat-in-1 through adat-in-8 - ADAT inputs
• pcm-playback-1 through pcm-playback-N - DAW playback channels

Usage

# Run the mixer
./sessionmixer run

# Inspect device topology
./sessionmixer topology

# Show routing endpoints
./sessionmixer topology --routing

# Show mixes
./sessionmixer topology --mixes

# Show level meters
./sessionmixer topology --meters

UI Layout

Each cue mix appears as a collapsible section containing:

• Output VU meters - Shows the mix output levels and configured outputs
• Mute button - Disconnects outputs (routes to "Off") when muted
• Device faders - One fader per device with input VU meters

VU Waterfall: Click on any channel title (device name or output label) to toggle a scrolling level history display beside the VU meter. The waterfall shows level over time, with newest samples at the bottom scrolling upward.

Behavior

• Stereo ganging - Stereo mix pairs (A+B, C+D, etc.) automatically gang faders
• Mute - Routes outputs to "Off" and saves current routing for restore
• Startup - Reads hardware routing state; if routing doesn't match expected, mix starts muted
• Bidirectional sync - External changes are reflected in the UI

License

MIT