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, μ-law, a-law, and ADPCM voice compression.
Sometimes referred to as μ-law format or Unix Audio Format.
The μ-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 support all audio codecs commonly used in the AU format.

Import and ExportImport and Export

  • Import[""] imports an AU file, returning a sound object.
  • Export["",expr] exports a sound object to an AU file encoded using 8-bit pulse code modulation.
  • Import[""] gives an expression of the form Sound[SampledSoundList[data,r]].
  • Export["",expr] creates an AU file from the sound object expr.
  • Import["",elem] imports the specified element from an AU file.
  • Import["",{elem,suba,subb,}] imports a subelement.
  • Import["",{{elem1,elem2,}}] imports multiple elements.
  • The import format can be specified with Import["file","AU"] or Import["file",{"AU",elem,}].
  • Export["",expr,elem] creates an AU file by treating expr as specifying element elem.
  • Export["",{expr1,expr2,},{{elem1,elem2,}}] treats each as specifying the corresponding .
  • Export["",expr,opt1->val1,] exports expr with the specified option elements taken to have the specified values.
  • Export["",{elem1->expr1,elem2->expr2,},"Rules"] uses rules to specify the elements to be exported.
  • See the reference pages for full general information on Import and Export.
  • ImportString and ExportString support the AU audio 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:
  • "Data"raw audio samples, given as a list of lists of real numbers, each sublist representing an individual audio channel
    "SampledSoundList"AU file given as SampledSoundList
    "Sound"Sound object that plays as the sound
  • The element corresponds to the first argument of SampledSoundList.
  • Multiple channels are represented as an array of audio samples.
  • Import and Export use the element by default for AU files.
  • Advanced Import element:
  • "SampleRate"number of amplitude samples per second and channel


  • General option:
  • SampleRateAutomaticnumber of audio 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 is set to a value n which 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.
  • 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"μ-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.

ExamplesExamplesopen allclose all

Basic Examples  (1)Basic Examples  (1)

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

Click for copyable input
Click for copyable input
Introduced in 1999