Audio File Format Specifications

File Description: AIFF, AIFF-C sound file
File Extension: Commonly .aif, sometimes .aiff or .aifc
File Byte Order: Big-endian, although some (little used) formats contain little-endian sound data

Prof. Peter Kabal, MMSP Lab, ECE, McGill University: Last update: 2011-01-03

AIFF / AIFF-C Specifications

The AIFF and the later AIFF-C specifications came from Apple Computer. This format is used on SGI machines. The latest data formats from Apple Computer are supported by the QuickTime player from Apple.

The AIFF and AIFF-C file formats use IFF chunks, each chunk consisting of a chunk identifier, chunk length and chunk data.

• AIFF
  • Original AIFF-1.3 specification, 1989-01-04 from Audio IFF Specification 1.3.
    Local copy: AIFF-1.3.pdf
• AIFF-C
  • AIFF-C specifications, 1991-08-26 (from ftp---ftp.sgi.com-sgi-aiff-c.9.26.91.ps.Z).
        Local copy: AIFF-C.9.26.91.pdf
  • Apple Computer documentation:
    • General information on AIFF/AIFF-C sound files in the Sound Manager documentation, 1998-04 (from MacOS_Sound.pdf, see pages 663-670).
      Local copy: MacOS_Sound-extract.pdf (extract)
    • Incidental information on the new compression types, 1999-07 (from QT4Reference.pdf, see pages 136-144)
      Local copy: QT4Reference-extract.pdf (extract)
• An implementation for reading and writing AIFF and AIFF-C files is available as part of the Audio File Library Project.

Data Types

AIFF files support only PCM data. They can specify any bit depth within a container which has a size which is rounded up to a multiple of 8 bits. Thus they can specify, for instance, 18 bits in a 24-bit container. The data in the container is left justified and zero padded. Data can be read as if it were the full precision of the container. The chunk information and the data (in most cases) is in big-endian byte order.

AIFF-C files can specify a compression type in the COMM chunk. The compression type is "NONE" for PCM data. The compression type is accompanied by a printable name. The following is a table of common compression types.

Differences Between AIFF and AIFF-C Files

• The identifier changes from "AIFF" to "AIFC".
• The FVER chunk appears only in AIFF-C files.
• AIFF-C files adds the compression type fields to the COMM chunk.

Notes

• More information on compression codes recognized by Apple Computer are in the header files AIFF.h and Sound.h in the QuickTime developer kit: QuickTime Windows SDK.
• Information on SGI's compression codes is found in the header files dmedia/audiofile.h, dmedia/dm_audio.h, and dmedia/dm_audioutil.h.
• Other compression types appear in aiff c information.
• Many of the compression schemes listed in the above sources are now considered obsolete. Of the codes for sample-by-sample coding, the following are still relevant: "NONE", "ulaw", "alaw", "fl32" and "fl64". Some systems also recognize the uppercase versions of these names.
• Float values in the Apple Computer schemes are normalized by default to a full-scale value of one.
• Apple maps Microsoft ACM formats into a compression code of the form "ms??" where the second two characters are the Microsoft Audio Compression Manager (ACM) code. For instance, Microsoft ADPCM, with ACM value of 1, is mapped to the code "ms\x00\x01".
• Apple Computer's QuickTime player recognize only the Apple compression types. Although "ALAW" and "ULAW" contain identical sound samples to the "alaw" and "ulaw" formats and were in use long before Apple introduced the new codes, QuickTime does not recognize them.
• The AIFF/AIFF-C specifications allow for the local chunks to occur in any order. However, most commonly the sound data itself (SSND chunk) occurs at the end of the file.
• The sampling frequency in the COMM chunk is stored as an 80-bit IEEE float value.

Sample AIFF/AIFC Files