Application programming interface for audio software in Apple's macOS and iOS
Audio Units (AU) are a system-level plug-in architecture provided by Core Audio in Apple's macOS and iOS operating systems. Audio Units are a set of application programming interface (API) services provided by the operating system to generate, process, receive, or otherwise manipulate streams of audio in near-real-time with minimal latency. It may be thought of as Apple's architectural equivalent to another popular plug-in format, Steinberg's Virtual Studio Technology (VST).
Audio Units allows sound file audio time stretching and pitch scaling (e.g., timestretch), sample rate conversion, and streaming over a local area network. It also comes with a set of AU plug-ins such as EQ filters, dynamic processors, delay, reverb, and a Soundbank Synthesizer Instrument.