The full form of AU is Audio Units which is system level architecture in Apple Computers .It is a set of API services used for transmission of audio in near real time.
Audio Units allows sound file with different options like audio time stretching and pitch scaling (e.g.timestretch), sample rate conversion, and streaming over a Local Area Network. It comes with a set of AU plug-ins like EQ filters, dynamic processors, delay, reverb, and a Soundbank Synthesizer Instrument.
Audio Units are used in Apple applications such as GarageBand, Soundtrack Pro, Logic Express, Logic Pro, Logic Pro X, Final Cut Pro, audio software developed for macOS such as Amadeus Pro, Ardour, Audio Hijack, Digital Performer, REAPER, and Studio One.
en.m.wikipedia.org/wiki/Audio_Units
AU File Specifications
The AU file format uses a simple extensible header, followed by data. The minimum length of header is 28 bytes.
| Offset | Length | Type | Contents |
| 0 | 4 | character | File magic “.snd” |
| 4 | 4 | unsigned integer | Offset to start of data |
| 8 | 4 | unsigned integer | Number of bytes of data |
| 12 | 4 | unsigned integer | Data format code |
| 16 | 4 | unsigned integer | Sampling rate |
| 20 | 4 | unsigned integer | Number of channels |
| 24 | – | character | Optional text information (minimum 4 bytes) |
Features of Audio units :
- Access== read-only, write-only or read/write only
- Scopes==input, output and global in iOS
- Data type==programmatic
Advantages of Audio units :
- Audio Units are the software modules used for instance, virtual instruments and audio effects which can be used by any audio application that supports AU plug-ins.
- By using Finale, we can take the advantage of audio plug-in architecture, allows Finale to load virtual instruments (e.g., Garritan instruments) and audio effects (e.g., Ambience Reverb) without having rely on a separate application to host them.
- AU is also an extension which is used in for a sound file program belongs to Sun, Next and DEC. This extension is basically used in UNIX. Spark audio is an another name for AU file format. AU files is of three parts :
1. Audio data
2. Text from header
3. An annotation block
Disadvantages of Audio units:-
- Editing in the project which contains Audio unit plug-ins can lead to timing issues
- Maximum number of audio unit that can be used in a project depends on the device in use
- Loading complex audio units can leads some time even on new devices
First AU file format maintained by apple and was introduced by Sun Microsystems. It is also the standard audio file format for the Java programming language. All AU files ends with a .au extension.
Sample AU file
Audio file format specifications
Sun. au sound file format
https://en.m.wikipedia.org/wiki/Au_file_format