MPEG-4 Structured Audio

MPEG-4 Structured Audio is an ISO/IEC standard for describing sound. It was published as subpart 5 of MPEG-4 Part 3 (ISO/IEC 14496-3:1999) in 1999.[1][2][3][4]

It allows the transmission of synthetic music and sound effects at very low bit rates (from 0.01 to 10 kbit/s), and the description of parametric sound post-production for mixing multiple streams and adding effects to audio scenes. It does not standardize a particular set of synthesis methods, but a method for describing synthesis methods.

The sound descriptions generate audio when compiled (or interpreted) by a compliant decoder. MPEG-4 Structured Audio consists of the following major elements:

  • Structured Audio Orchestra Language (SAOL), an audio programming language. SAOL is historically related to Csound and other so-called Music-N languages. It was created by an MIT Media Lab grad student named Eric Scheirer while he was studying under Barry Vercoe during the 1990s.
  • Structured Audio Score Language (SASL) - is used to describe the manner in which algorithms described in SAOL are used to produce sound.
  • Structured Audio Sample Bank Format (SASBF) - allows for the transmission of banks of audio samples to be used in 'wavetable' sample-based synthesis (based on SoundFont and DownLoadable Sounds)[5]
  • A normative Structured Audio scheduler description - it is the supervisory run-time element of the Structured Audio decoding process.
  • MIDI support - provides important backward-compatibility with existing content and authoring tools.

MPEG-4 Structured Audio was cited by CNN as one of the top-25 innovations to arise at the Media Laboratory.[6]

See also

References
  1. ISO (1999). "ISO/IEC 14496-3:1999 - Information technology -- Coding of audio-visual objects -- Part 3: Audio". ISO. Retrieved 2009-10-06.
  2. ISO/IEC JTC 1/SC 29/WG 11 (1998-05-15), ISO/IEC FCD 14496-3 Subpart 5 - Information Technology - Coding of Audiovisual Objects – Low Bitrate Coding of Multimedia Objects, Part 3: Audio, Subpart 5: Structured Audio, Final Committee Draft, N2203SA (PDF), retrieved 2009-10-10
  3. D. Thom, H. Purnhagen, and the MPEG Audio Subgroup (October 1998). "MPEG Audio FAQ Version 9 - MPEG-4". chiariglione.org. Archived from the original on 2009-09-26. Retrieved 2009-10-06.CS1 maint: multiple names: authors list (link)
  4. Heiko Purnhagen (2001-06-01). "The MPEG-4 Audio Standard: Overview and Applications". Heiko Purnhagen. Retrieved 2009-10-07.
  5. Scheirer, Eric D.; Ray, Lee (1998). "Algorithmic and Wavetable Synthesis in the MPEG-4 Multimedia Standard". Audio Engineering Society Convention 105, 1998. CiteSeerX 10.1.1.35.2773. 2.2 Wavetable synthesis with SASBF: The SASBF wavetable-bank format had a somewhat complex history of development. The original specification was contributed by E-Mu Systems and was based on their “SoundFont” format [15]. After integration of this component in the MPEG-4 reference software was complete, the MIDI Manufacturers Association (MMA) approached MPEG requesting that MPEG-4 SASBF be compatible with their “Downloaded Sounds” format [13]. E-Mu agreed that this compatibility was desirable, and so a new format was negotiated and designed collaboratively by all parties.
  6. "THE BIG I: MIT Media Lab Turns 25". CNN.


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