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.{{cite web | url=http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=25035 | title=ISO/IEC 14496-3:1999 - Information technology -- Coding of audio-visual objects -- Part 3: Audio | author=ISO | publisher=ISO | year=1999 | access-date=2009-10-06| author-link=International Organization for Standardization }}{{Cite FTP | url=ftp://ftp.tnt.uni-hannover.de/pub/MPEG/audio/mpeg4/documents/w2203/w2203sa.pdf | title=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 | author=ISO/IEC JTC 1/SC 29/WG 11 | date=1998-05-15 | server=FTP server | url-status=dead | access-date=2009-10-10}}{{cite web | url=http://www.chiariglione.org/mpeg/faq/mp4-aud/mp4-aud.htm | title=MPEG Audio FAQ Version 9 - MPEG-4 | author=D. Thom, H. Purnhagen, and the MPEG Audio Subgroup | publisher=chiariglione.org | date=October 1998 | access-date=2009-10-06 | archive-url=https://web.archive.org/web/20090926231123/http://www.chiariglione.org/mpeg/faq/mp4-aud/mp4-aud.htm | archive-date=2009-09-26 | url-status=dead }}{{cite web | url=http://140.130.175.70/html/mpeg4/sound.media.mit.edu/mpeg4/audio/general/index.html#aes106 | title=The MPEG-4 Audio Standard: Overview and Applications | author=Heiko Purnhagen | publisher=Heiko Purnhagen | date=2001-06-01 | access-date=2009-10-07}} {{Dead link|date=October 2010|bot=H3llBot}}

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 MIT Media Lab grad student 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)

{{cite journal

| last1 = Scheirer | first1 = Eric D.

| last2 = Ray | first2 = Lee

| title = Algorithmic and Wavetable Synthesis in the MPEG-4 Multimedia Standard

| periodical= Audio Engineering Society Convention 105, 1998

| date = 1998

| quote = 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.

| citeseerx = 10.1.1.35.2773

}}

• 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.{{cite news | url=http://newsroom.blogs.cnn.com/2010/10/12/the-big-i-mit-media-lab-turns-25/ | archive-url=https://archive.today/20130102052008/http://newsroom.blogs.cnn.com/2010/10/12/the-big-i-mit-media-lab-turns-25/ | url-status=dead | archive-date=January 2, 2013 |title=THE BIG I: MIT Media Lab Turns 25 | work=CNN}}