Audio Interchange File Format
Audio Interchange File Format is an audio file format standard used for storing sound data for personal computers and other electronic audio devices. The format was developed by Apple Inc. in 1988 based on Electronic Arts' Interchange File Format and is most commonly used on Apple Macintosh computer systems.
The audio data in most AIFF files is uncompressed pulse-code modulation. This type of AIFF file uses much more disk space than lossy formats like MP3—about 10 MB for one minute of stereo audio at a sample rate of 44.1 kHz and a bit depth of 16 bits. There is also a compressed variant of AIFF known as AIFF-C or AIFC, with various defined compression codecs.
In addition to audio data, AIFF can include loop point data and the musical note of a sample, for use by hardware samplers and musical applications.
The file extension for the standard AIFF format is .aiff or .aif. For the compressed variants it is supposed to be .aifc, but.aiff or.aif are accepted as well by audio applications supporting the format.
AIFF on Mac OS X
With the development of the Mac OS X operating system, Apple created a new type of AIFF which is, in effect, an alternative little-endian byte order format.Because the AIFF architecture has no provision for alternative byte order, Apple used the existing AIFF-C compression architecture, and created a "pseudo-compressed" codec called sowt. The only difference between a standard AIFF file and an AIFF-C/sowt file is the byte order; there is no compression involved at all.
Apple uses this new little-endian AIFF type as its standard on Mac OS X. When a file is imported to or exported from iTunes in "AIFF" format, it is actually AIFF-C/sowt that is being used. When audio from an audio CD is imported by dragging to the Mac OS X Desktop, the resulting file is also an AIFF-C/sowt. In all cases, Apple refers to the files simply as "AIFF", and uses the ".aiff" extension.
For the vast majority of users this technical situation is completely unnoticeable and irrelevant. The sound quality of standard AIFF and AIFF-C/sowt are identical, and the data can be converted back and forth without loss. Users of older audio applications, however, may find that an AIFF-C/sowt file will not play, or will prompt the user to convert the format on opening, or will play as static.
All traditional AIFF and AIFF-C files continue to work normally on Mac OS X, and many third-party audio applications as well as hardware continue to use the standard AIFF big-endian byte order.
AIFF Apple Loops
Apple has also created another recent extension to the AIFF format in the form of Apple Loops used by GarageBand and Logic Pro, which allows the inclusion of data for pitch and tempo shifting by an application in the more common variety, and MIDI-sequence data and references to GarageBand playback instruments in another variety.AppleLoops use either the.aiff or.caf extension regardless of type.
Data format
An AIFF file is divided into a number of chunks. Each chunk is identified by a chunk ID more broadly referred to as FourCC.Types of chunks found in AIFF files:
- Common Chunk
- Sound Data Chunk
- Marker Chunk
- Instrument Chunk
- Comment Chunk
- Name Chunk
- Author Chunk
- Copyright Chunk
- Annotation Chunk
- Audio Recording Chunk
- MIDI Data Chunk
- Application Chunk
- ID3 Chunk
Metadata
Common compression types
AIFF supports only uncompressed PCM data. AIFF-C also supports compressed audio formats, that can be specified in the "COMM" chunk. The compression type is "NONE" for PCM audio data. The compression type is accompanied by a printable name. Common compression types and names include, but are not limited to:| Compression type | Compression name | Data | Source |
| NONE | not compressed | PCM, big-endian | Apple Inc. |
| sowt | not compressed | PCM, little-endian | Apple Inc. |
| fl32 | 32-bit floating point | IEEE 32-bit float | Apple Inc. |
| fl64 | 64-bit floating point | IEEE 64-bit float | Apple Inc. |
| alaw | ALaw 2:1 | 8-bit ITU-T G.711 A-law | Apple Inc. |
| ulaw | μLaw 2:1 | 8-bit ITU-T G.711 μ-law | Apple Inc. |
| ALAW | CCITT G.711 A-law | 8-bit ITU-T G.711 A-law | SGI |
| ULAW | CCITT G.711 u-law | 8-bit ITU-T G.711 μ-law | SGI |
| FL32 | Float 32 | IEEE 32-bit float | SoundHack & Csound |
| ADP4 | 4:1 Intel/DVI ADPCM | Stéphane Tavenard AmigaOS | |
| ima4 | IMA 4:1 | ||
| ACE2 | ACE 2-to-1 | Apple IIGS ACE | |
| ACE8 | ACE 8-to-3 | ||
| DWVW | Delta with variable word width | TX16W Typhoon | |
| MAC3 | MACE 3-to-1 | Apple Inc. | |
| MAC6 | MACE 6-to-1 | Apple Inc. | |
| Qclp | Qualcomm PureVoice | Qualcomm | |
| QDMC | QDesign Music | QDesign | |
| rt24 | RT24 50:1 | Voxware | |
| rt29 | RT29 50:1 | Voxware | |
| SDX2 | Square-Root-Delta | Big-endian | 3DO / MAC |