Halo

Volume control for macOS Multi-Output Devices.
F11 / F12 keys, scroll-wheel, and a custom HUD — works when macOS's native volume refuses to.

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What this is

macOS deliberately disables the keyboard volume keys and the menu-bar slider when a Multi-Output Device is selected as system output. If you drive two Apple Studio Displays, monitors + headphones, or any aggregate output, you've hit the grey-slider problem.

Halo is a menu-bar app that fixes this. It intercepts F11 / F12 / mute and writes volume to each sub-device of the aggregate directly, so your speakers change together.

This is a fork of rlxone/MultiSoundChanger by Dmitry Medyuho (Apache 2.0), modernised for macOS Sequoia / macOS 15+ and with additional quality-of-life features. The original project did the hard part — figuring out the CoreAudio incantations for writing to aggregate sub-devices. Without it, Halo wouldn't exist.

Features on top of upstream

• Custom volume HUD that replaces Apple's broken private OSDManager (no chiclets bar on macOS Sequoia+).
• 32 finer volume steps (~3% each) instead of the OS default 16.
• Scroll-wheel on the menu-bar icon to adjust volume without reaching for keys.
• One-click "Create Halo Speakers" — auto-builds a Multi-Output aggregate from connected Apple Studio Displays, skipping Audio MIDI Setup.
• Volume persistence — each sub-device's level is saved to UserDefaults on change and restored at launch, avoiding the cold-boot "slammed to 100%" surprise.
• Launch at Login toggle via SMAppService.
• Universal binary — native on Apple Silicon and Intel.
• Stable self-signed code-signing identity so macOS's TCC keeps Accessibility grants across rebuilds during development.
• Modern macOS compat fixes — storyboard module resolution after PRODUCT_NAME rename, aggregate-device drift handling, bundled OSD.framework binary replaced with the current SDK stub so arm64 linking works.

Halo vs native macOS

	Native macOS	Halo
Volume keys on Multi-Output Device	❌	✅
Scroll-wheel volume on menu bar	❌	✅
Custom volume HUD (macOS 15+)	❌ broken	✅
Auto-create aggregate for Studio Displays	❌	✅
Volume persistence across reboots	⚠️ unreliable	✅
Launch at Login	✅	✅
Free	✅	✅
Signed by Apple	✅	❌ self-signed (see Limitations)

Screenshot

The Halo menu: output-device picker with the one-click Create Halo Speakers aggregate, Launch at Login toggle, and shortcuts to Sound Preferences and Audio Devices.

The custom HUD that fires on F11/F12 or scroll-wheel. Replaces Apple's private OSDManager, which no longer renders reliably on macOS Sequoia.

Install

Requires macOS 13 (Ventura) or later.

Option 1 — Build from source

git clone https://github.com/flight-william/MultiSoundChanger.git -b rebrand/halo
cd MultiSoundChanger
pod install                          # CocoaPods is required
./scripts/setup-codesign-cert.sh     # one-time: creates a self-signed cert
./scripts/build-and-install.sh       # build Release, sign, copy to /Applications

On first launch, grant Accessibility permission when prompted (Privacy & Security → Accessibility).

Option 2 — Use a pre-built binary

No public release binary yet. Build from source, or ask the author.

Set up a Multi-Output Device

If you don't already have one in Audio MIDI Setup, you have two paths:

• Apple Studio Displays (two or more) — click Halo's menu-bar icon → Create Halo Speakers. One click.
• Any other combination — open Audio MIDI Setup, + → Create Multi-Output Device, tick the devices you want, right-click → Use This Device for Sound Output. Halo will pick it up.

Usage

• Click Halo's menu icon, pick your Multi-Output Device from the list.
• Press F11 / F12 to adjust volume, F10 to mute.
• Or scroll on your trackpad while hovering near Halo's icon.
• Optional: toggle Launch at Login in the menu.

Limitations

This fork is a personal project. Please read before using:

• Not signed by Apple — Halo is signed with a self-signed certificate, not an Apple Developer ID. Gatekeeper will warn on first launch. If you build from source yourself, you control the signing identity; if you trust a pre-built binary, you're trusting whoever built it.
• Not notarized — Apple's malware-scan warrant isn't applied, because that requires a paid Developer Program membership.
• Uses Apple's private OSD.framework for the bridging header. Private APIs can change between macOS versions; a rebuild against the new SDK usually fixes breaks, but no guarantees.
• "Create Halo Speakers" only auto-matches Apple Studio Displays by device name. Other combinations require manual aggregate creation in Audio MIDI Setup (Halo still controls volume on them fine).
• Hobby scale — single maintainer, no auto-update, no bug tracker, no guarantee of future macOS compatibility.

If you need a supported commercial alternative, SoundSource by Rogue Amoeba is signed, notarized, and supported.

Credits

• rlxone/MultiSoundChanger by Dmitry Medyuho — Apache License 2.0. The upstream project, still the canonical implementation.
• MediaKeyTap by Nicholas Hurden — MIT. Used for global media-key interception.

License

Apache License 2.0 (inherited from upstream MultiSoundChanger). See LICENCE.

Original copyright © 2017 Dmitry Medyuho. Fork modifications © 2026 flight-william.