Audio Unit Validation on macOS: What auval, the AU Cache and Logic Are Really Doing

Why "Installed" and "Available in Logic" Are Different Things

You run an installer, it says success, and the plugin still isn't in Logic. Or it shows up in Ableton but Logic lists it as failed. Nothing is broken at random here: macOS keeps a system-wide registry of Audio Units, hosts query that registry, and Logic adds its own validation pass on top. Once you know the three layers, almost every AU problem becomes diagnosable in a few minutes.

Layer 1: The Component on Disk

A classic Audio Unit (AU v2) is a .component bundle in one of two places:

• /Library/Audio/Plug-Ins/Components/ - available to every user. Most installers put plugins here.
• ~/Library/Audio/Plug-Ins/Components/ - only for your user account.

Inside the bundle, the Info.plist declares one or more Audio Components with three four-character codes: type, subtype and manufacturer. The type tells hosts what the plugin is:

• aufx - effect
• aumu - instrument (music device)
• aumf - music effect (an effect that also receives MIDI)
• aumi - MIDI processor
• augn - generator

These three codes are the plugin's identity everywhere on the system. Projects reference them, caches are keyed by them, and validation tools take them as arguments.

Audio Units v3 work differently: they are app extensions bundled inside an application, sandboxed, and registered when the containing app is installed in /Applications and launched once. If an AUv3 plugin is missing, open its host app first.

Layer 2: The System Registry and the AU Cache

macOS doesn't make every host scan the Components folders on its own. A system process, AudioComponentRegistrar, keeps track of installed components and caches what it found in ~/Library/Caches/AudioUnitCache/ (the file is com.apple.audiounits.cache). Hosts ask the registrar what is installed.

When that cache is stale - after an interrupted install, a manual file copy, or an update that changed a component's version - hosts may not see a new plugin, or may see an old version. The reset is safe and quick:

1. Quit every audio application.
2. Delete the contents of ~/Library/Caches/AudioUnitCache/.
3. Run killall -9 AudioComponentRegistrar in Terminal. macOS restarts it automatically.
4. Open your DAW. It will rebuild the list, which can take a while with a large plugin collection.

Layer 3: Validation with auval

Apple ships a command-line validator, auval, that loads an Audio Unit and exercises it: instantiation, initialization, supported channel layouts and sample rates, parameter handling, rendering, and clean teardown. Logic runs the same kind of test before it lets a plugin into its menus.

Two commands cover most situations:

auval -a
auval -v aufx XXXX YYYY

The first lists every Audio Unit macOS knows about, with its three codes. Find your plugin's line and copy them. The second validates that one plugin - replace aufx, XXXX and YYYY with its type, subtype and manufacturer. A clean run ends with AU VALIDATION SUCCEEDED. A failure prints exactly which test failed, which is far more useful than Logic's one-word "failed".

The Usual Reasons Validation Fails

Wrong architecture

On Apple Silicon, a native host can't load an Intel-only binary. Check what a plugin contains with:

lipo -archs "/Library/Audio/Plug-Ins/Components/Name.component/Contents/MacOS/Name"

x86_64 arm64 means Universal. x86_64 alone means Intel-only. The fix is the vendor's Universal build. The fallback is running the host under Rosetta (Get Info on the app, then Open using Rosetta), which switches every plugin in that session to Intel mode and costs performance.

A dialog the validator can't click

Validation runs without a user. A plugin that opens an authorization window, a "new version available" prompt or a first-run setup during instantiation can time out or fail. Authorize the plugin in its own app or license manager first, then rescan.

Gatekeeper and quarantine

Files downloaded from the internet carry a quarantine attribute, and macOS can refuse to load unsigned or unnotarized code inside a host. xattr -l on the bundle shows whether com.apple.quarantine is set. Removing it is a security decision - only ever do it for plugins from a vendor you trust, and prefer a signed installer from that vendor instead.

Missing support files

Many plugins need resources outside the component: sample content, a license file, a shared framework in /Library/Application Support/. A partial uninstall that left the component but removed the support folder produces a plugin that validates in one host and crashes in another. Reinstall from the vendor's installer rather than copying components by hand.

Logic's Plug-in Manager: The Safe Front End

Logic keeps its own record of validation results and exposes it in Logic Pro → Settings → Plug-in Manager. Use it instead of deleting caches blindly:

• Select failed plugins and choose Reset & Rescan Selection after you've fixed the cause.
• The Use checkbox lets you force-enable a plugin that failed validation. That is occasionally justified for a plugin that fails one strict test but works in practice - and a common cause of crashes when it isn't. Save often if you do.
• Uncheck plugins you never use. Logic won't load them, which shortens startup and removes them from menus.

A Five-Minute Diagnosis Routine

1. Is the component where you expect it, and is it Universal? (ls the Components folder, then lipo -archs.)
2. Does macOS list it? (auval -a.) If not, reset the AU cache.
3. Does it validate? (auval -v with its codes.) Read the failing test.
4. Fix the cause - Universal build, authorization, reinstall - then Reset & Rescan in Logic.
5. Only then consider forcing it with Use.

Keeping a record of which plugins failed and why also pays off: when a scan crashes on one plugin, ProducerGrid marks that exact plugin path so the next scan skips it instead of crashing again, and you can see at a glance which formats of a plugin are affected.