APM44 Bridge

APM44 Bridge is for producers who track and mix at 44.1 kHz but monitor on AirPods Max connected over USB-C, which run at 48 kHz. It presents a virtual 44.1 kHz Core Audio output device to the DAW and resamples to the headphones in user space, so the session rate never has to change.

Download

Download the latest release (signed, notarized DMG containing a signed PKG): GitHub Releases.

Requirements: macOS 14 or newer, Apple silicon or Intel Mac, AirPods Max over USB-C. See the end-user install guide.

Features

• A virtual 44.1 kHz output device, APM44 Bridge, that any DAW can select.
• High-quality resampling to 48 kHz (libsamplerate) with automatic clock-drift correction.
• Picks your USB-C AirPods Max automatically and lists other compatible 48 kHz outputs.
• Buffering presets (Low, Balanced, Safe) and resampling Quality (Standard, High, Best).
• Lives in the menu bar, with Start/Stop, Open at login and guided Setup.
• Updates itself: checks at launch, or on demand with Check for Updates…; app and driver always update together.
• Clear guidance when the audio driver needs a reload or reinstall.

Quick start

1. Open the DMG from the latest release and run the installer. It installs the app and its audio driver, then opens the app.
2. In the DAW, select APM44 Bridge as the audio output. In Cubase, assign Control Room Monitor L/R to APM44 Bridge — see the Cubase first-run guide.
3. In the menu-bar app, pick the AirPods output and press Start.

How it works

Cubase 15 / DAW at 44.1 kHz
  -> APM44 Bridge HAL output device at 44.1 kHz
  -> apm44-bridge user-space daemon
  -> AirPods Max USB-C at 48 kHz

The headphones are not retuned to 44.1 kHz. APM44 Bridge presents a virtual 44.1 kHz Core Audio output device upstream, resamples in user space, handles clock drift, and plays to the physical 48 kHz endpoint.

Tested with Cubase 15. Logic Pro and Ableton Live are not yet validated — see the DAW validation matrix.

Status

Component	Status
HAL driver APM44Bridge.driver	44.1 kHz virtual output device
Bridge daemon apm44-bridge	libsamplerate conversion and drift control
Menu bar app APM44 Bridge	virtual-device mode, latency presets, first-run checks, visible Quit control
Release packaging	Developer ID signed PKG inside signed/notarized DMG

Development

Requirements:

• macOS 14 or newer
• Xcode 16.x, or Xcode 15.4+
• CMake 3.28+
• XcodeGen (brew install cmake xcodegen)

git clone --recurse-submodules https://github.com/Niko96-dotcom/apm44-bridge.git
cd apm44-bridge
bash scripts/ci.sh

Useful focused checks:

bash scripts/check-secrets.sh
bash scripts/verify-app-build.sh
bash scripts/rebuild-and-open-app.sh
bash scripts/verify-menu-bar.sh
bash scripts/ci-soak.sh

For a local UI instance with separate preferences that leaves the installed app running, use bash scripts/rebuild-and-open-app.sh --isolated. See local verification and performance for its audio-device limits, repeatable measurements, worktree setup, and the Xcode compiler-probe workaround if a build stalls during discovery.

Hardware pre-flight checks (default --hal: APM44 Bridge @ 44100 + AirPods @ 48000; BlackHole not required):

bash scripts/verify-devices.sh --hal
bash scripts/verify-devices.sh --fallback  # legacy BlackHole route only
bash scripts/verify-hal-driver.sh

Release

End users should install the signed, notarized DMG from GitHub Releases. Source builds are useful for development, but a reliable public HAL install on modern macOS requires Developer ID signing and notarization.

On a maintainer Mac with Developer ID Application and Installer certificates plus a configured notarytool profile, build the public PKG-in-DMG release with:

export SIGN_ID="Developer ID Application: Your Name (TEAMID)"
export INSTALLER_SIGN_ID="Developer ID Installer: Your Name (TEAMID)"
export NOTARY_PROFILE="AC_NOTARY"
bash scripts/release-all.sh

See docs/release.md for manual signing, notarization, stapling, and troubleshooting steps.

Documentation

Doc	Purpose
install.md	End-user install and daily use
first-run-cubase.md	Cubase 15 Control Room setup
cubase-soak.md	30+ minute QA soak
daw-matrix.md	DAW validation matrix
release.md	Signing and notarization
architecture.md	Architecture map (entry points, modules, contracts, state owners) and how the driver, shm ring, daemon and app fit together
hal-driver.md	HAL driver and shared memory IPC
menu-bar-app.md	Menu bar app architecture
mvp-routing.md	BlackHole fallback path

BlackHole Fallback

The fallback route is:

DAW -> BlackHole 2ch at 44.1 kHz -> apm44-bridge -> AirPods at 48 kHz

BlackHole is optional, external, and not bundled. See docs/blackhole-prerequisite.md.

Security

Please report suspected vulnerabilities privately. See SECURITY.md.

License

APM44 Bridge is open source under the MIT License. Third-party notices are in NOTICE and third_party/README.md.