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AudioUnit Tutorial - How to add AUv2 support to your VST 3 plug-in

On this page:

Adding the AudioUnit Version 2 Target

Related pages:

AudioUnit v2 Wrapper

You'll find the source for this tutorial in the tutorial repository

In this tutorial you will learn how to add AudioUnit Version 2 support to your VST 3 plug-in.

First of all, you need a VST 3 plug-in project. For this tutorial we have generated one via the VST 3 Project Generator from the SDK.

Adding the AudioUnit Version 2 Target

Obtaining the required AudioUnit SDK

The AudioUnit Version 2 target needs the official AudioUnit SDK from Apple. As of this writing you can find it on GitHub: https://github.com/apple/AudioUnitSDK

How you obtain and store the SDK is up to you, for the reproducibility of this tutorial, we will download it via CMake when generating the project. So we add the following text to the CMakeLists.txt directly before we include the VST 3 SDK.

include(FetchContent)
FetchContent_Declare(
	AudioUnitSDK
	GIT_REPOSITORY https://github.com/apple/AudioUnitSDK.git
	GIT_TAG        HEAD
)
FetchContent_MakeAvailable(AudioUnitSDK)
FetchContent_GetProperties(
	AudioUnitSDK
	SOURCE_DIR SMTG_AUDIOUNIT_SDK_PATH
)

It is important to set the SMTG_AUDIOUNIT_SDK_PATH variable to tell the VST 3 SDK where to find the AudioUnit SDK.

Creating the property list

For AudioUnit Version 2 you need a manufacturer OSType registered with Apple. How to do this is out of the scope for this tutorial, please search the web on how this is done.

Besides the manufacturer OSType you also need a subtype OSType which you can choose by yourself. Both the manufacturer and subtype account for the uniqueness of your AudioUnit Version 2.

Now you can generate the required property list file:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
	<key>CFBundleDevelopmentRegion</key>
	<string>English</string>
	<key>CFBundleExecutable</key>
	<string>$(EXECUTABLE_NAME)</string>
	<key>CFBundleIdentifier</key>
	<string>$(PRODUCT_BUNDLE_IDENTIFIER)</string>
	<key>CFBundleName</key>
	<string>$(PRODUCT_NAME)</string>
	<key>CFBundleInfoDictionaryVersion</key>
	<string>6.0</string>
	<key>CFBundlePackageType</key>
	<string>BNDL</string>
	<key>CFBundleSignature</key>
	<string>????</string>
	<key>CFBundleVersion</key>
	<string>1.0</string>
	<key>CSResourcesFileMapped</key>
	<string>yes</string>
	<key>AudioComponents</key>
	<array>
		<dict>
			<key>factoryFunction</key>
			<string>AUWrapperFactory</string>
			<key>description</key>
			<string>AudioUnit Tutorial</string>
			<key>manufacturer</key>
			<string>Stgb</string>
			<key>name</key>
			<string>Steinberg: AudioUnit Tutorial</string>
			<key>subtype</key>
			<string>0002</string>
			<key>type</key>
			<string>aufx</string>
			<key>version</key>
			<integer>1</integer>
		</dict>
	</array>
</dict>
</plist>

Make sure to change the strings for description, manufacturer, name, subtype and type. The type must be one of:

aufx (Audio Effect)
aumu (Instrument)
aumf (Audio Effect with MIDI Input/Output)

If you build an audio effect you also need to add the supported channel layouts to the list:

<key>AudioUnit SupportedNumChannels</key>
<array>
	<dict>
		<key>Outputs</key>
		<string>2</string>
		<key>Inputs</key>
		<string>2</string>
	</dict>
	<dict>
		<key>Outputs</key>
		<string>2</string>
		<key>Inputs</key>
		<string>1</string>
	</dict>
	<dict>
		<key>Outputs</key>
		<string>1</string>
		<key>Inputs</key>
		<string>1</string>
	</dict>
</array>

Save it to a file called au-info.plist inside the resource directory.