AVaudioUnitMBS events

Targets macOS
1

This question is for Christian Schmitz, who has urged me to ask publicly so it may benefit others (or anyone else who may know).

I’m using the AVAudioUnitSamplerMBS class to load virtual instruments into my MIDI apps. I want to get notified if the user changes the controls or the preset. The only event I see that could be useful is:

PropertyListener(ID as UInt32, Scope as UInt32, Element as UInt32)

How do I get a list of potential properties to listen for. I’d like to simply start by getting the preset the user has selected so I can set it up the next time that instrument is loaded. Thanks.

2

Well, I found in the headers:

#pragma mark - AUSampler

/*!
	@enum			Apple AUSampler Property IDs
	@abstract		The collection of property IDs for the Apple Sampler audio unit.
 
	@discussion		The AUSampler audio unit lets a client create an editable, interactive
					sampler synthesizer instrument.
 
	@constant		kAUSamplerProperty_LoadInstrument
	@discussion			Scope:			Global
						Value Type:		AUSamplerInstrumentData
						Access:			Write
							Load an instrument from an external DLS or Soundfont2 bank file, or from other file formats.
 
	@constant		kAUSamplerProperty_LoadAudioFiles
	@discussion			Scope:			Global
						Value Type:		CFArrayRef
						Access:			Write
							Create a new preset from a list of audio file paths.  The CFArray should contain a set
							of CFURLRefs, one per file.  The previous preset will be completely cleared.
 */
CF_ENUM(AudioUnitPropertyID) {
	// range (4100->4999)
	kAUSamplerProperty_LoadInstrument				= 4102,
	kAUSamplerProperty_LoadAudioFiles				= 4101
};
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3

See also more properties:

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4

And I found CurrentPreset:

CF_ENUM(AudioUnitPropertyID) {
	//kAudioUnitProperty_SetInputCallback		= 7 -> deprecated
	kAudioUnitProperty_SRCAlgorithm				= 9, // see kAudioUnitProperty_SampleRateConverterComplexity
	kAudioUnitProperty_MIDIControlMapping		= 17, // see ParameterMIDIMapping Properties
	kAudioUnitProperty_CurrentPreset			= 28, // see PresentPreset

	kAudioUnitProperty_ParameterValueName		= kAudioUnitProperty_ParameterStringFromValue,
	kAudioUnitProperty_BusCount					= kAudioUnitProperty_ElementCount,

	kAudioOfflineUnitProperty_InputSize			= kAudioUnitOfflineProperty_InputSize,
	kAudioOfflineUnitProperty_OutputSize		= kAudioUnitOfflineProperty_OutputSize
};

and below

	@constant		kAudioUnitProperty_PresentPreset
						Scope:				Global/Part
						Value Type:			AUPreset
						Access:				read/write

						This property replaces the deprecated CurrentPreset property, due to the ambiguity of
						ownership of the CFString of the preset name in the older CurrentPreset property. 
						With PresentPreset the client of the audio unit owns the CFString when it retrieves the
						preset with PresentPreset and is expected to release this (as with ALL properties 
						that retrieve a CF object from an audio unit).
	kAudioUnitProperty_PresentPreset				= 36,
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6

Thanks, Christian. I guess I’ve got some reading to do.