AU (.au)


    Registered MIME type: audio/basic
    AU audio format.
    Used for digital audio in computer and telecommunication systems and on the web.
    Supports a variety of audio codecs, including lossless uncompressed PCM, -law, a-law, and ADPCM voice compression.
    Sometimes referred to as -law format or Unix Audio Format.
    The -law algorithm is a standard method for compressing the dynamic range of a signal.
    AU is an acronym derived from Audio.
    Binary file format.
    Supports various sampling frequencies and an arbitrary number of channels.
    Identical to the SND format.
    Developed by Sun Microsystems in 1992.

Import and Export

  • Import[""] imports an AU file, returning an audio object.
  • Import["",elem] imports the specified element from an AU file.
  • The import format can be specified with Import["file","AU"] or Import["file",{"AU",elem,}].
  • Export["",expr] exports an audio or sound object to an AU file.
  • Sound objects including notes are rasterized to sampled audio.
  • See the reference pages for full general information on Import and Export.
  • ImportString and ExportString support the AU format.


  • General Import elements:
  • "Elements"list of elements and options available in this file
    "Rules"full list of rules for each element and option
    "Options"list of rules for options, properties, and settings
  • Data representation elements:
  • "Audio"audio signal given as an Audio object
    "AudioFile"audio signal given as an out-of-core Audio object
    "Data"raw audio samples, given as a list of real numbers, each sublist representing an individual audio channel
    "SampledSoundList"audio signal given as a SampledSoundList object
    "Sound"audio signal given as a Sound object
  • Import and Export use the "Audio" element by default for AU files.
  • Advanced Import element:
  • "Duration"duration of the audio given in seconds
    "Length"number of samples
    "SampleDepth"number of bits used to store every sample
    "SampleRate"number of amplitude samples per second and channel
  • Multiple channels are represented as an array of audio samples.


  • Import and Export option:
  • IncludeMetaInformationAllwhether to include meta-information
    SampleRateAutomaticnumber of samples per second for each channel
  • Detailed properties and settings:
  • "AudioChannels"Automaticthe number of audio channels in the file
    "AudioEncoding""Integer8"how samples are encoded
  • If the sample rate is not specified when exporting to AU, the highest sample rate occurring in the exported sound is used, and all sounds are resampled as necessary.
  • If the number of channels is unspecified, the highest number of simultaneous channels is taken, and silence is inserted if necessary.
  • If "AudioChannels" is set to a value n that is less than the number of channels to be exported, only the first n channels are exported.
  • The AU format supports PCM (pulse code modulation) and ADPCM (adaptive differential pulse code modulation) codecs and various other audio encoding algorithms.
  • "AudioEncoding" can be set to any of the following codecs:
  • "Integer8"8-bit PCM
    "Integer16"16-bit PCM
    "Integer24"24-bit PCM
    "Integer32"32-bit PCM
    "Real32"32-bit IEEE floating point
    "Real64"64-bit IEEE floating point
    "aLaw"a-Law 4-bit PCM (ITU-T G.711)
    "uLaw"-Law 4-bit PCM (ITU-T G.711)
    "G721-32"32 kbps ADPCM (ITU G.721)
    "G723-24"G.723 encoding at 24 kbps
    "G723-40"G.723 encoding at 40 kbps
  • Not all codecs support arbitrary sample rates and channel specifications.


Basic Examples  (1)

Use Play to create a short sound sample and export it to AU:

Click for copyable input
Click for copyable input

See Also

"AIFF"  "FLAC"  "SND"  "WAV"

Introduced in 1999
| Updated in 2016