Audio Units (AU) are a system-level

plug-in Plug-in, plug in or plugin may refer to: * Plug-in (computing), a software component that adds a specific feature to an existing computer program ** Audio plug-in, adds audio signal processing features ** Photoshop plugin, a piece of software that ...

architecture provided by

Core Audio Core Audio is a low-level API for dealing with sound in Apple's macOS and iOS operating systems. It includes an implementation of the cross-platform OpenAL. Apple's Core Audio documentation states that "in creating this new architecture on Ma ...

Apple An apple is a round, edible fruit produced by an apple tree (''Malus'' spp.). Fruit trees of the orchard or domestic apple (''Malus domestica''), the most widely grown in the genus, are agriculture, cultivated worldwide. The tree originated ...

macOS macOS, previously OS X and originally Mac OS X, is a Unix, Unix-based operating system developed and marketed by Apple Inc., Apple since 2001. It is the current operating system for Apple's Mac (computer), Mac computers. With ...

and

iOS Ios, Io or Nio (, ; ; locally Nios, Νιός) is a Greek island in the Cyclades group in the Aegean Sea. Ios is a hilly island with cliffs down to the sea on most sides. It is situated halfway between Naxos and Santorini. It is about long an ...

operating systems. Audio Units are a set of

application programming interface An application programming interface (API) is a connection between computers or between computer programs. It is a type of software Interface (computing), interface, offering a service to other pieces of software. A document or standard that des ...

(API) services provided by the

operating system An operating system (OS) is system software that manages computer hardware and software resources, and provides common daemon (computing), services for computer programs. Time-sharing operating systems scheduler (computing), schedule tasks for ...

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 Steinberg Media Technologies GmbH (trading as Steinberg; ) is a German musical software and hardware company based in Hamburg. It develops software for writing, recording, arranging and editing music, most notably Cubase, Nuendo, and Dorico. It ...

Virtual Studio Technology Virtual Studio Technology (VST) is an audio plug-in software interface that integrates software synthesizers and effects units into digital audio workstations. VST and similar technologies use digital signal processing to simulate traditional rec ...

(VST). Because of the many similarities between Audio Units and VST, several commercial and free wrapping technologies are available (e.g
Symbiosis
and

FXpansion FXpansion is a Ltd company that produces music software including Geist2, Strobe2, Tremor, Etch, Bloom, Maul and DCAM Dynamics. History FXpansion is a company that develops music software, and was founded in 1999 in London, United Kingd ...

br>VST-AU Adapter
.

Celemony Software Celemony Software GmbH is a German musical software company that specializes in digital audio pitch correction software. It produces Melodyne, a popular audio pitch modification tool similar to Auto-Tune, although the program itself is manual t ...

and

PreSonus PreSonus Audio Electronics, Inc. (often known and styled as PreSonus) is an American manufacturer of professional audio equipment and software, used to create, record, mix, and master music and other audio. This includes their line of digital a ...

have also developed the

Audio Random Access Audio Random Access (commonly abbreviated to ARA) is an extension for audio plug-in interfaces, such as AU, VST and RTAS, allowing them to exchange a greater amount of audio information with digital audio workstation (DAW) software. It was dev ...

(ARA) extension, which works for both AU and VST, allowing greater integration between the plug-ins and DAW software.

Use

Audio Units allows sound file

audio time stretching and pitch scaling Time stretching is the process of changing the speed or duration of an audio signal without affecting its pitch. Pitch scaling is the opposite: the process of changing the pitch without affecting the speed. Pitch shift is pitch scaling implement ...

(e.g., timestretch),

sample rate In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave to a sequence of "samples". A sample is a value of the signal at a point in time and/or ...

conversion, and streaming over a

local area network A local area network (LAN) is a computer network that interconnects computers within a limited area such as a residence, campus, or building, and has its network equipment and interconnects locally managed. LANs facilitate the distribution of da ...

. It also comes with a set of AU plug-ins such as EQ filters, dynamic processors, delay, reverb, and a Soundbank Synthesizer Instrument. AU are used by Apple applications such as

GarageBand GarageBand is a software application by Apple Inc., Apple for macOS, iPadOS, and iOS devices that allows users to create music or Podcast, podcasts. It is a lighter, amateur-oriented offshoot of Logic Pro. GarageBand was originally released for ...

Soundtrack Pro Soundtrack Pro is a discontinued music composing and audio editing application made by Apple Inc. It included a collection of just over 5,000 royalty free professional instrument loops and sound effects for use. The software was featured in the ...

Logic Express Logic Pro is a proprietary digital audio workstation (DAW) and MIDI sequencer software application for the macOS platform developed by Apple Inc. It was originally created in the early 1990s as Notator Logic, or Logic, by German software devel ...

Logic Pro Logic Pro is a proprietary digital audio workstation (DAW) and MIDI sequencer software application for the macOS platform developed by Apple Inc. It was originally created in the early 1990s as Notator Logic, or Logic, by German software devel ...

Logic Pro X Logic Pro is a proprietary digital audio workstation (DAW) and MIDI sequencer software application for the macOS platform developed by Apple Inc. It was originally created in the early 1990s as Notator Logic, or Logic, by German software devel ...

Final Cut Pro Final Cut Pro (often abbreviated FCP or FCPX) is a professional non-linear video-editing application initially developed by Macromedia, and, since 1998, by Apple as part of its pro apps collection. Final Cut Pro allows users to import, edit, a ...

MainStage MainStage is a music application developed by Apple Inc. designed for use in live performance. Features MainStage works in a similar way and has a similar user interface to Logic Pro, although the focus is on live use rather than features li ...

and most 3rd party audio software developed for

such as

Ableton Live Ableton Live is a digital audio workstation for macOS and Windows developed by the German company Ableton. In contrast to many other software sequencers, Live is designed to be an instrument for live performances as well as a tool for compos ...

, Amadeus Pro, Ardour,

Audio Hijack Rogue Amoeba Software, Inc. is a software company that produces audio software, specializing in applications for audio capture for the Macintosh platform. Rogue Amoeba's best-known products are Audio Hijack and Audio Hijack Pro (both now known ...

DaVinci Resolve DaVinci Resolve is a proprietary color grading, color correction, visual effects, and audio post-production video editing application for macOS, Windows, and Linux, developed by Australian company Blackmagic Design. It was originally deve ...

Digital Performer Digital Performer is a digital audio workstation and music sequencer software package published by Mark of the Unicorn (MOTU) of Cambridge, Massachusetts for the Apple Macintosh and Microsoft Windows platforms. Ancestry In 1984, Mark of the U ...

, Gig Performer,

REAPER A reaper is a farm implement that reaps (cuts and often also gathers) crops at harvest when they are ripe. Usually the crop involved is a cereal grass, especially wheat. The first documented reaping machines were Gallic reapers that were used ...

, and Studio One.

Competing technologies

* Avid's Avid Audio eXtension (a successor to the RTAS format) *

Digidesign Avid Audio (formerly Digidesign) is an American digital audio technology company. It was founded in 1984 by Peter Gotcher and Evan Brooks. The company began as a project to raise money for the founders' band, selling EPROM chips for drum machin ...

Real Time AudioSuite Real-Time AudioSuite (RTAS) is an audio plug-in format developed by Digidesign, currently Avid Technology, for their Pro Tools LE and Pro Tools M-Powered systems, although they can be run on Pro Tools HD and Pro Tools TDM systems. RTAS plug-i ...

(now obsolete) *

LADSPA The Linux Audio Developer's Simple Plugin API (LADSPA) is an application programming interface (API) standard for handling audio filters and audio signal processing effects, licensed under LGPL-2.1-or-later. Originally designed through consensus ...

and

Disposable Soft Synth Interface Disposable Soft Synth Interface (DSSI) is a virtual instrument (software synthesizer) plugin architecture for use by music sequencer applications. It was designed for applications running under Linux, although there is nothing specific to Linux ...

(DSSI) for

Linux Linux ( ) is a family of open source Unix-like operating systems based on the Linux kernel, an kernel (operating system), operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically package manager, pac ...

* LV2 (crossplatform successor to LADSPA) *

Microsoft Microsoft Corporation is an American multinational corporation and technology company, technology conglomerate headquartered in Redmond, Washington. Founded in 1975, the company became influential in the History of personal computers#The ear ...

DirectX Microsoft DirectX is a collection of application programming interfaces (APIs) for handling tasks related to multimedia, especially game programming and video, on Microsoft platforms. Originally, the names of these APIs all began with "Direct" ...

References

{{OS X Music software plugin architectures macOS APIs