A macOS 26 menu-bar readout for the monitor level, mute state, active speaker
group, and Input 1 preamp gain of the Focusrite Scarlett 16i16 4th Gen (USB
1235:821b). It reads the state directly from the hardware; Focusrite Control 2
is not required. Input 1 gain appears as a read-only row in the status menu.
Changing the Input 1 gain knob also shows its value in a native menu-bar
popover for two seconds.
The app submits one USB interrupt transfer and sleeps inside libusb while the
device is idle. Hardware notifications trigger reads of masterVolume,
muteSwitch, altSwitch, and the device-map-discovered Input 1 preamp gain.
USB hot-plug callbacks handle unplug and replug. There is no value polling or
repeating timer.
The build requires the macOS 26 Command Line Tools and Homebrew's libusb.
The resulting app statically links libusb.
brew install libusb
make verifyThe app bundle is written to build/ScarlettVolume.app.
open build/ScarlettVolume.appThe only menu item is Quit.
Made with Codex and GPT-5.6 Sol. Use at your own risk.