KH Volume

KH Volume is a macOS menu bar application designed to control the volume of Neumann KH DSP studio monitors. It is especially useful when your speakers are connected via S/PDIF coaxial digital input or USB, where the standard macOS volume keys no longer map to your monitors.

Instead of adjusting the system volume slider, KH Volume directly drives the network DSP level of your speakers using Sennheiser Sound Control (SSC) over IPv6. This provides a practical and precise way to change the listening level and toggle mute directly from your Mac's menu bar.

Thanks to Thorsten Schwinn and the contributors of khtool — the open-source Python tool that communicates with Georg Neumann KH speakers over SSC. KH Volume is a native macOS shell around a bundled khvol helper that builds on vendored khtool (MIT). Without that project, this app would not exist.

Supported Monitors

If your KH monitors are connected to your local network via Ethernet (built-in port or adapter) and support SSC, KH Volume can seamlessly manage their levels. This includes popular models across the Neumann KH DSP lineup: KH 80 DSP, KH 120 II, KH 150, KH 150 AES67, and KH 750 DSP.

How it works

1. Your Mac and the speakers share a network connection (usually Ethernet to the speaker’s RJ45 port).
2. KH Volume runs a bundled khvol helper (Python + khtool) to send SSC commands over the LAN.
3. The app displays the current DSP level in the menu bar, featuring a popover similar to the native macOS Sound interface.
4. Optional global shortcuts (default ⌥= / ⌥-) allow you to adjust the level without opening the popover.

Important: The control mechanism operates entirely over the network control plane, independent of the audio bitstream. This means your Mac can output pristine audio via a digital S/PDIF connection while the volume level is managed separately over Ethernet via SSC.

Features

• Menu bar level display and slider for quick access
• Mute toggle functionality
• Network interface picker (supports USB Ethernet adapters, built-in LAN, etc.)
• Per-app volume cap (“volume limit”) and customizable step sizes (1 / 3 / 6 dB)
• Global keyboard shortcuts (customizable in Sound Settings)
• Open at Login support (requires a signed app in /Applications)
• Left/right level mismatch warning for stereo pairs

Requirements

• macOS 14 or later
• Neumann KH DSP monitors reachable on your LAN via SSC (IPv6 link-local)
• A Mac network interface capable of reaching the speakers (e.g., USB–Ethernet adapter, en15, en0)
• To build from source: Xcode Command Line Tools / Swift 5.9+, Python 3.12+ (for the bundled helper only)

Install (release)

Pre-built signed releases may be published separately. To build locally:

./scripts/build-khvol-helper.sh
./scripts/build-app-bundle.sh
open "dist/KH Volume.app"

For distribution signing and notarization, see scripts/sign-app.sh.

Development

# Build PyInstaller helper (first time or after KhVolume/Helper/ changes)
./scripts/build-khvol-helper.sh

# Run the app
cd KhVolume && swift run

# Optional: run helper CLI from source
./KhVolume/Scripts/khvol-dev interfaces
./KhVolume/Scripts/khvol-dev scan --config-dir ~/.khvol-test -i en15

App data and scan cache: ~/Library/Application Support/KHVolume/

Smoke test (hardware or offline-tolerant):

export KHVOL_INTERFACE=en15   # your USB-LAN interface name
./scripts/smoke-test.sh

Troubleshooting

Symptom	Things to check
Menu bar shows !	Speaker off, wrong network interface, or no route to the speaker
No speakers in Network list	Cable/link down; pick the interface that has link (ifconfig)
Level does not change	Confirm --scan finds devices; try the interface where khtool works
Open at Login fails	Install a Developer ID–signed KH Volume.app in /Applications
Left/right levels differ	Use decrease-only until matched, or enable “allow increase when mismatched” in settings

Project layout

KhVolume/              Swift menu bar app (Swift Package Manager)
  Sources/             App UI and logic
  Helper/              khvol CLI + vendor/khtool (bundled into the app)
  Scripts/             khvol-dev — run CLI from source without PyInstaller
scripts/               build-app-bundle.sh, sign-app.sh, smoke-test.sh

Credits

• Speaker control protocol: SSC (Sennheiser Sound Control), used by Georg Neumann GmbH KH DSP products.
• Low-level tool: khtool by Thorsten Schwinn et al. (vendored under KhVolume/Helper/vendor/).
• App: native SwiftUI menu bar shell around the bundled khvol helper.

License

KH Volume is released under the MIT License. See NOTICES for bundled third-party components (including khtool and pyssc).

This project is not affiliated with Georg Neumann GmbH, Sennheiser, or Neumann. Neumann product names are trademarks of their respective owners. Use of SSC to control your hardware is at your own risk.