MPEG-4 Structured Audio

Short description: Audio Encoding Standard

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

* MPEG-4

## References

1. ↑ ISO (1999). "ISO/IEC 14496-3:1999 - Information technology -- Coding of audio-visual objects -- Part 3: Audio". ISO. http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=25035.
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, ftp://ftp.tnt.uni-hannover.de/pub/MPEG/audio/mpeg4/documents/w2203/w2203sa.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. http://www.chiariglione.org/mpeg/faq/mp4-aud/mp4-aud.htm.
4. ↑ Heiko Purnhagen (2001-06-01). "The MPEG-4 Audio Standard: Overview and Applications". Heiko Purnhagen. http://140.130.175.70/html/mpeg4/sound.media.mit.edu/mpeg4/audio/general/index.html#aes106. [|permanent dead link|dead link}}]
5. ↑ Scheirer, Eric D.; Ray, Lee (1998). "Algorithmic and Wavetable Synthesis in the MPEG-4 Multimedia Standard". Audio Engineering Society Convention 105, 1998. "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. http://newsroom.blogs.cnn.com/2010/10/12/the-big-i-mit-media-lab-turns-25/.

## External links

* MPEG-4 Structured Audio Developer Tools
* MPEG-4 Part 3 Subpart 5: Structured Audio, Final Committee Draft, N2203SA, 1998
* The MPEG-4 Structured Audio standard - Eric D. Scheirer, MIT Media Laboratory
* Official MPEG web site
* [1]

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