Audio Interchange File Format
Audio Interchange File Format
The audio data
in most AIFF files is uncompressed pulse-code modulation
(PCM). 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
, 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
spelled backwards). 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 (including on the new Intel-based hardware), 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.
Apple Loops use either the .aiff (or .aif) or .caf extension regardless of type.
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 (required)
- Sound Data Chunk (required)
- Marker Chunk
- Instrument Chunk
- Comment Chunk
- Name Chunk
- Author Chunk
- Copyright Chunk
- Annotation Chunk
- Audio Recording Chunk
- MIDI Data Chunk
- Application Chunk
- ID3 Chunk
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:
- ^ a b Apple Computer, Inc. (1989-01-04), Audio Interchange File Format, A Standard for Sampled Sound Files, Version 1.3 (PDF), retrieved 2010-03-21
- ^ P. Kabal (2005-03-15). "Audio File Format Specifications - AIFF / AIFF-C Specifications". McGill University. Retrieved 2010-03-21.
- ^ Mac OS X Reference Library
- ^ Supported Audio File and Data Formats in Mac OS X
- ^ "Technical Q&A QTMRF04: QuickTime Sound". Apple. 1995-05-01. Retrieved 2009-11-09.
- ^ "Logic Studio - Plug-ins & Sounds". Apple. Retrieved 2010-04-30.
- ^ Audio File Format Specifications
- ^ "AIFF Tagging".
- ^ Tom Erbe (1999). "AIFF-C Compression Types and Names". Archived from the original on 2006-06-20. Retrieved 2010-03-21.
- ^ "JSTOR/Harvard Object Validation Environment - AIFF-hul Module". 2005-05-09. Archived from the original on 2010-06-29. Retrieved 2010-03-21.
Last edited on 16 June 2021, at 15:59
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