AU (.au)

Background & Context

    • 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 & 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 following reference pages for full general information:
  • Import, Exportimport from or export to a file
    CloudImport, CloudExportimport from or export to a cloud object
    ImportString, ExportStringimport from or export to a string
    ImportByteArray, ExportByteArrayimport from or export to a byte array

Import Elements

  • General Import elements:
  • "Elements" list of elements and options available in this file
    "Summary"summary of the file
    "Rules"list of rules for all available elements
  • 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"Integer16"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: