This chapter describes the function-like macros declared in the
Audio header file. You can use these macros to work with an audio unit parameter’s display types—one of the attributes specified by the flags field in the
Audio data structure.
Audio unit properties, part of the audio unit plug-in interface, are key-value pairs that declare attributes or behavior such as audio data stream format, latency, or connection from one audio unit to another. Properties are typically non-time-varying, not directly settable by the user, and changeable only before an audio unit is initialized. This document describes audio unit property identifiers and their accompanying values.
You access audio unit properties using the Audio Unit framework’s “Get” and “Set” functions, described in Audio Unit Component Services. These functions are:
So-called generic audio unit properties are those that can apply to any audio unit. There are also Apple-specific properties that apply only to Apple-supplied audio units. This document describes both. Apple reserves property IDs from 0 through 63999; you may use property IDs above this range.
In addition to its value, the attributes of an audio unit property are as follows:
Scope—the programmatic context, within an audio unit, that the property applies to. A property applies to one or more scopes, as described in this document. The audio unit scopes in iOS are Input, Output, and Global. In macOS, audio units have additional, MIDI-related scopes: Group, Part, and Note.
Data type—the programmatic data type for the property’s value.
Access—read-only, write-only, or read/write.