FocusMute

Hotkey mute control for Focusrite Scarlett 4th Gen interfaces.

FocusMute monitors your system microphone's mute state and reflects it on your Focusrite Scarlett interface LEDs in real time. When you mute, the input number indicator LEDs ("1", "2") turn your chosen color (default: red). When you unmute, they are restored to their firmware colors (green for the selected input, white for unselected). Metering halos and all other LEDs are never touched. It runs as a system tray app on Windows and Linux with hotkey support, or as a CLI on both platforms.

Features

Global hotkey toggle (default: Ctrl+Shift+M) with sound feedback
Configurable mute color per input (any hex color or named color)
Auto-reconnect on device disconnect and graceful startup without device
Schema-driven multi-model support (auto-discovers unknown Scarlett 4th Gen devices)
Settings GUI (tray app) and TOML config file
Extensible via shell hook commands, desktop notifications, and device serial targeting

Supported Devices

Device	Support
Scarlett 2i2 4th Gen	Full (hardcoded LED profile)
Scarlett Solo / 4i4 4th Gen	Auto-discovery via firmware schema extraction
Scarlett 16i16 / 18i16 / 18i20 4th Gen	Untested — likely works on Windows; requires unimplemented FCP Socket protocol on Linux

The small 4th Gen models (Solo, 2i2, 4i4) use the TRANSACT/hwdep protocol which FocusMute fully implements. The big models (16i16, 18i16, 18i20) use a different communication path on Linux (FCP Socket via a daemon process). On Windows they likely work through the same SwRoot driver, but this is unverified without hardware.

The probe command can detect any Scarlett 4th Gen device and extract its LED layout from firmware. Use map to interactively verify the predicted layout.

Installation

Windows

Download the MSI installer or standalone .exe from Releases.

focusmute.exe -- system tray app (tray icon, hotkey, settings dialog)
focusmute-cli.exe -- CLI-only binary

Linux

Prerequisites: libpulse0 (PulseAudio), libgtk-3-0 (GTK 3), libappindicator3-1 (system tray), libegl1 (egui rendering). PipeWire works transparently via the pipewire-pulse compatibility layer — ensure pipewire-pulse or libpulse0 is installed.

Debian / Ubuntu / Mint:

sudo dpkg -i focusmute_*.deb
sudo apt-get install -f   # resolve any missing deps

This installs both binaries (focusmute tray app + focusmute-cli), udev rules, and desktop entries.

Arch / Fedora / other (from tar.gz):

sudo install -m 755 focusmute focusmute-cli /usr/local/bin/
sudo install -m 644 99-focusrite.rules /etc/udev/rules.d/
sudo udevadm control --reload-rules && sudo udevadm trigger --subsystem-match=usb

See dist/linux/README-linux.md for full details and desktop entry setup.

Usage

Tray App (Windows + Linux)

Launch focusmute (or focusmute.exe on Windows). It sits in the system tray, monitors your mic, and updates LEDs automatically. Right-click for the menu (Status, Toggle Mute, Settings, Reconnect Device, Quit). The global hotkey (default: Ctrl+Shift+M) toggles mute. If no Scarlett device is connected at startup, the app starts in "Disconnected" mode and automatically connects when the device is plugged in. On exit, inputs are automatically unmuted and LEDs restored to their normal state. The tray app logs to focusmute.log in the config directory (info level by default; override with RUST_LOG env var). On startup, any config parse errors or validation warnings are shown as a desktop notification.

Linux notes: The tray app uses GTK 3. Global hotkeys work on X11; on Wayland they may not function (use the tray menu instead).

CLI

focusmute-cli [--verbose|-v] [--config <path>] <command>

Flag	Description
`--verbose`, `-v`	Enable debug-level logging to stderr
`--config <path>`	Load settings from a custom TOML file instead of the default location

Command	Description
`monitor`	Watch mic mute state and update LEDs in real time
`status`	Show device, microphone, and config status (`--json`)
`config`	Show current configuration and file paths (`--json`, `--edit` to open in `$VISUAL`/`$EDITOR`)
`devices`	List connected Focusrite devices (`--json`)
`probe`	Detect device and extract firmware schema (`--dump-schema` for full JSON)
`map`	Interactive LED identification (lights one index at a time)
`predict`	Predict LED layout from a schema JSON file (no hardware needed)
`descriptor`	Dump raw descriptor bytes (`--offset`, `--size`)
`mute`	Mute the default capture device
`unmute`	Unmute the default capture device

Configuration

Config file location:

Windows: %APPDATA%\Focusmute\config.toml
Linux: ~/.config/focusmute/config.toml

Created with defaults on first run. Example:

[indicator]
mute_color = "#FF0000"
mute_inputs = "all"
# Per-input colors (optional):
# [indicator.input_colors]
# 1 = "#FF0000"
# 2 = "#0000FF"

[keyboard]
hotkey = "Ctrl+Shift+M"

[sound]
sound_enabled = true
mute_sound_volume = 1.0
unmute_sound_volume = 1.0
mute_sound_path = ""
unmute_sound_path = ""

[system]
autostart = false
device_serial = ""
notifications_enabled = false

[hooks]
on_mute_command = ""
on_unmute_command = ""

Setting	Default	Description
`[indicator].mute_color`	`"#FF0000"`	Hex color or name (e.g. `"red"`, `"#00FF00"`)
`[indicator].mute_inputs`	`"all"`	Which inputs to indicate: `"all"`, `"1"`, `"2"`, `"1,2"`
`[indicator.input_colors]`	`{}`	Per-input mute colors (TOML table, e.g. `1 = "#FF0000"`)
`[keyboard].hotkey`	`"Ctrl+Shift+M"`	Global hotkey (tray app; X11 only on Linux)
`[sound].sound_enabled`	`true`	Play sound on mute/unmute
`[sound].mute_sound_volume`	`1.0`	Volume for mute sound (0.0–1.0)
`[sound].unmute_sound_volume`	`1.0`	Volume for unmute sound (0.0–1.0)
`[sound].mute_sound_path`	`""`	Custom WAV path (empty = built-in)
`[sound].unmute_sound_path`	`""`	Custom WAV path (empty = built-in)
`[system].autostart`	`false`	Start on login (tray app)
`[system].device_serial`	`""`	Preferred device serial (empty = auto-select first)
`[system].notifications_enabled`	`false`	Show desktop notification on mute/unmute
`[hooks].on_mute_command`	`""`	Shell command to run on mute (empty = disabled)
`[hooks].on_unmute_command`	`""`	Shell command to run on unmute (empty = disabled)

Architecture

Workspace Layout

focusmute/
├── Cargo.toml                          Workspace root
├── LICENSE                             Apache-2.0
├── .cargo/config.toml                  Build configuration
├── .github/workflows/
│   ├── ci.yml                          Lint, test, build (Windows + Linux)
│   └── release.yml                     Tagged release with MSI + .deb
├── dist/linux/
│   ├── README-linux.md                 Linux install guide (included in tar.gz)
│   ├── 99-focusrite.rules              udev rules for USB access
│   ├── focusmute.desktop               Desktop entry (tray app)
│   ├── focusmute-cli.desktop           Desktop entry (CLI)
│   └── debian/                         Maintainer scripts (postinst)
├── crates/focusmute-lib/               Core library
│   ├── Cargo.toml
│   └── src/
│       ├── lib.rs                      Public API re-exports
│       ├── audio.rs                    Mic mute monitoring (WASAPI / PulseAudio)
│       ├── config.rs                   TOML settings + validation
│       ├── context.rs                  Device resolution pipeline
│       ├── device.rs                   USB communication (ScarlettDevice trait)
│       ├── error.rs                    Unified error types
│       ├── hooks.rs                    Shell command hooks (on_mute/on_unmute)
│       ├── layout.rs                   LED layout prediction from schema
│       ├── models.rs                   Hardcoded device profiles
│       ├── monitor.rs                  Mute state machine (debounce + decide)
│       ├── offsets.rs                  Descriptor offset calculations
│       ├── protocol.rs                 USB protocol constants
│       ├── reconnect.rs                Exponential backoff
│       ├── schema.rs                   Firmware schema extraction
│       └── led/
│           ├── mod.rs                  LED module re-exports
│           ├── color.rs                Color parsing (#RRGGBB <-> 0xRRGGBB00)
│           ├── ops.rs                  LED device operations
│           └── strategy.rs             Mute visualization strategy
└── crates/focusmute/                   CLI + tray app
    ├── Cargo.toml                      Defines focusmute + focusmute-cli binaries
    ├── build.rs                        Embeds app icon into .exe (Windows, via winresource)
    ├── wix/                            WiX MSI installer sources
    └── src/
        ├── main.rs                     Tray app entry point (Windows + Linux)
        ├── main_cli.rs                 CLI entry point
        ├── cli/                        CLI subcommands
        │   ├── mod.rs                  Command enum, dispatch, shared helpers
        │   ├── config_cmd.rs           config subcommand
        │   ├── descriptor.rs           descriptor subcommand
        │   ├── devices.rs              devices subcommand
        │   ├── map.rs                  map subcommand
        │   ├── monitor.rs              monitor subcommand
        │   ├── mute.rs                 mute/unmute subcommands
        │   ├── predict.rs              predict subcommand
        │   ├── probe.rs                probe subcommand
        │   └── status.rs              status subcommand
        ├── icon.rs                     Embedded PNG icon + app icon helper
        ├── notification.rs             Desktop notifications (WinRT / notify-rust)
        ├── settings_dialog/            Settings dialog (egui / eframe)
        │   ├── mod.rs                  Shared helpers, dispatcher, SoundPreviewPlayer
        │   └── ui.rs                   Cross-platform egui UI + build_and_validate_config
        ├── tray/                       System tray app
        │   ├── mod.rs                  Platform dispatcher + single-instance
        │   ├── shared.rs               Shared event loop (PlatformAdapter trait)
        │   ├── state/                  Tray state management
        │   │   ├── mod.rs              TrayState, TrayResources, message dispatch
        │   │   ├── icon.rs             Icon loading + caching (CachedIcon)
        │   │   ├── menu.rs             Menu, notifications, mute UI updates
        │   │   └── hotkey.rs           Hotkey registration + re-registration
        │   ├── windows.rs              Windows adapter: Win32 message pump
        │   └── linux.rs                Linux adapter: GTK event loop
        └── sound.rs                    Pre-decoded audio playback

Crate Responsibilities

focusmute-lib is the core library. It owns all device communication, LED control, audio monitoring, configuration, and schema parsing. It has no UI dependencies and compiles on both Windows and Linux with platform-specific backends behind #[cfg] gates.

focusmute is the application layer. It provides two binaries:

focusmute -- system tray app for Windows and Linux (tray icon, hotkey, settings dialog, sound playback)
focusmute-cli -- cross-platform CLI with subcommands for monitoring, diagnostics, and device control

Module Map

Module	Responsibility	Key Types
`audio`	Mic mute monitoring	`MuteMonitor` trait, `WasapiMonitor`, `PulseAudioMonitor`
`config`	TOML settings + validation	`Config`, `IndicatorConfig`, `KeyboardConfig`, `SoundConfig`, `SystemConfig`, `HooksConfig`, `MuteInputs`
`context`	Device resolution pipeline	`DeviceContext`
`device`	USB communication	`ScarlettDevice` trait, `DeviceInfo`, `FirmwareVersion`
`error`	Unified errors	`FocusmuteError`, `DeviceError`, `AudioError`
`hooks`	Shell command hooks	`run_action_hook`
`layout`	LED layout prediction	`PredictedLayout`, `PredictedLed`, `Confidence`
`led/color`	Color parsing	`parse_color`, `format_color`
`led/ops`	LED device operations	`apply_mute_indicator`, `clear_mute_indicator`, `restore_on_exit`
`led/strategy`	Mute visualization	`MuteStrategy`, `resolve_mute_strategy`
`models`	Hardcoded device profiles	`ModelProfile`, `HaloRange`, `detect_model`
`monitor`	Mute state machine	`MuteIndicator`, `MuteDebouncer`, `MonitorAction`
`offsets`	Descriptor offset calculations	`DeviceOffsets`
`protocol`	USB protocol constants	IOCTL codes, command codes, descriptor offsets, notify IDs
`reconnect`	Exponential backoff	`ReconnectState`
`schema`	Firmware schema extraction	`SchemaConstants`, `extract_schema`, `parse_schema`

Data Flow

The monitor loop follows a simple poll-decide-act pipeline:

Audio Backend ---poll---> MuteIndicator ---action---> LED ops ---USB---> Device
  (WASAPI /                (debounce +                (single-LED via
   PulseAudio)              decide)                    DATA_NOTIFY(8))
       ^                                                    |
       |                  ReconnectState                    |
       |                  (backoff on                       |
       +--- wait_for_change / 250ms timeout ---<--- disconnect detection)

The audio backend reports mute state changes (event-driven with 250ms polling fallback).
MuteIndicator debounces the signal (2-sample threshold) and emits ApplyMute, ClearMute, or NoChange.
LED ops translate the action into USB descriptor writes and DATA_NOTIFY(8) commands targeting number indicator LEDs.
On communication failure, ReconnectState manages exponential backoff until the device reappears.
On exit, inputs are unmuted (so the user isn't left silently muted) and number LEDs are restored to firmware colors by reading selectedInput (green for selected, white for unselected).

Key Design Decisions

Trait-based platform abstraction. ScarlettDevice and MuteMonitor are traits with platform-specific implementations. This keeps the core logic testable without hardware and makes adding new backends straightforward.
State machine over callbacks. MuteIndicator encapsulates debouncing and mute/unmute transitions as a pure state machine. It is decoupled from I/O -- the caller drives it by feeding mute samples and applying the resulting actions.
Schema-driven multi-model support. Known devices (Scarlett 2i2 4th Gen) have hardcoded ModelProfiles for zero-latency startup. Unknown Scarlett 4th Gen devices are discovered at runtime by extracting the firmware schema (base64 + zlib compressed JSON) and predicting the LED layout from it.
Minimal LED footprint. Mute indication uses the single-LED update mechanism (directLEDColour + directLEDIndex + DATA_NOTIFY(8)), targeting only the number indicator LEDs ("1", "2"). Metering halos, output LEDs, and button LEDs are never touched — the device continues normal operation.
Platform-abstracted tray loop. The PlatformAdapter trait injects platform-specific behavior (GTK vs Win32 event pumping, PulseAudio vs WASAPI monitoring) into a shared generic event loop (run_core<P>), eliminating ~80% code duplication between Windows and Linux tray implementations.

Building from Source

Prerequisites

Rust toolchain (stable)
Linux: libpulse-dev, pkg-config, libasound2-dev, libgtk-3-dev, libxdo-dev, libappindicator3-dev, libegl-dev
Windows cross-compile: gcc-mingw-w64-x86-64, x86_64-pc-windows-gnu target

Build

# Linux (native)
sudo apt-get install libpulse-dev pkg-config libasound2-dev libgtk-3-dev libxdo-dev libappindicator3-dev libegl-dev
cargo build --release

# Windows (cross-compile from Linux/WSL2)
sudo apt-get install gcc-mingw-w64-x86-64
rustup target add x86_64-pc-windows-gnu
cargo build --release --target x86_64-pc-windows-gnu

Output binaries:

Linux: target/release/focusmute, target/release/focusmute-cli
Windows: target/x86_64-pc-windows-gnu/release/focusmute.exe, focusmute-cli.exe

Test

cargo fmt --check                  # formatting
cargo clippy -- -D warnings        # lints
cargo test                         # unit + integration tests
cargo deny check advisories        # dependency vulnerability audit (requires cargo-deny)

cargo-deny is not bundled with the Rust toolchain — install it separately with cargo install cargo-deny.

Packaging

.msi

Requires WiX Toolset v3 (light.exe and candle.exe on PATH):

cargo install cargo-wix
cargo build --release --target x86_64-pc-windows-gnu
cargo wix -p focusmute --no-build --nocapture

Output: target/wix/focusmute-<version>-x86_64.msi

The MSI installs both binaries to Program Files\Focusmute, adds a Start Menu shortcut, and optionally adds the install directory to PATH. The WiX source is at crates/focusmute/wix/main.wxs.

.deb

cargo install cargo-deb
cargo build --release
cargo deb -p focusmute --no-build

Output: target/debian/focusmute_<version>-1_amd64.deb

The .deb installs both binaries to /usr/bin/, udev rules to /etc/udev/rules.d/, desktop entries to /usr/share/applications/, and runs postinst/postrm scripts to reload udev rules. Dependencies (libpulse0, libgtk-3-0, libappindicator3-1, libegl1) are declared automatically. The deb metadata is in crates/focusmute/Cargo.toml under [package.metadata.deb].

License

Copyright 2026 Martin Simon

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.

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Name		Name	Last commit message	Last commit date
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.cargo		.cargo
.github/workflows		.github/workflows
crates		crates
dist/linux		dist/linux
docs		docs
.gitignore		.gitignore
CHANGELOG.md		CHANGELOG.md
Cargo.lock		Cargo.lock
Cargo.toml		Cargo.toml
LICENSE		LICENSE
README.md		README.md
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deny.toml		deny.toml

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FocusMute

Features

Supported Devices

Installation

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Linux

Usage

Tray App (Windows + Linux)

CLI

Configuration

Architecture

Workspace Layout

Crate Responsibilities

Module Map

Data Flow

Key Design Decisions

Building from Source

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FocusMute

Features

Supported Devices

Installation

Windows

Linux

Usage

Tray App (Windows + Linux)

CLI

Configuration

Architecture

Workspace Layout

Crate Responsibilities

Module Map

Data Flow

Key Design Decisions

Building from Source

Prerequisites

Build

Test

Packaging

.msi

.deb

License

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