Sustainability of Digital Formats: Planning for Library of Congress Collections

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AES3 Digital Audio Interface, SMPTE Extensions

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name Format for Non-PCM Audio and Data in an AES3 Serial Digital Audio Interface (formal name); Non-PCM AES3 (common name)

Society of Motion Picture and Television Engineers (SMPTE) extensions to the AES3 interface that specify a method for transmitting AC-3 compressed audio (instead of the LPCM uncompressed audio specified in AES3) and other types of data. The SMPTE extensions permit the inclusion of, and picture-synchronize with, multichannel surround sound within the technical confines of television technology. AC-3 audio, also known as Dolby Digital, is used in theater systems, DVDs, and can be incorporated in MPEG-2 streams. The other types of data specified in the extensions include "null data" (to permit preamble sync codes to be inserted into the data stream) and time stamp data to support synchronization. Additional SMPTE specifications concern wrapping tracks encoded in what they call the AES3 format in MXF. See the list of Format specifications below.

The main thrust of AES3 and this extension thereof concerns cabling and the physical interface between devices (see Notes below). This Web site, however, is primarily devoted to encodings and file, wrapper, or bundling formats. At times, the SMPTE standards refers to AES3 as an encoding (e.g., SMPTE standard 382M, Mapping AES3 Streams and Broadcast Wave Audio to the MXF Generic Container) and this has led to its inclusion at this Web site.

The Wikipedia article on AES3 (consulted on March 8, 2011) reports that the specification is "officially known as AES3 and frequently called AES/EBU and also published as part of IEC 60958."

Production phase Most often used as a middle state ("post-production") or final state ("release, disseminated, broadcast") format.
Relationship to other formats
    Extension of AC-3, AC-3 Compressed Audio (Dolby Digital), Revision A
    Used by MPEG-2 program stream or file with MPEG-2 and AES3 Digital Audio Interface, SMPTE Extensions (Dolby and surround audio encoding). Not described at this Web site at this time.
    Used by MXF File, OP1a, AES3 Audio in Generic Container, not described at this Web site at this time.
    Used by MXF File, OP1a, SDTI-CP in Generic Container, not described at this Web site at this time.

Local use Explanation of format description terms

LC experience or existing holdings Not determined; Library collections include DVDs and are known to include files with MPEG-2 video with "layer II" audio streams.
LC preference Not determined.

Sustainability factors Explanation of format description terms

Disclosure Open standard. Developed by the Society of Motion Picture and Television Engineers (SMPTE), using an Audio Engineering Society (AES) standard as the basis.
    Documentation Covered by a variety of SMPTE and AES documents; see Format specifications below.
Adoption Appears to be widely adopted, apparently to the greatest degree for DVDs and MPEG-2 video streams; Comments welcome.
    Licensing and patents None on the interface specification; see also AC-3.
Transparency The interface specification is transparent; see also AC-3.
Self-documentation See AC-3.
External dependencies The AES3 specification used as a basis covers wiring and cable connectors.
Technical protection considerations None

Quality and functionality factors Explanation of format description terms

Normal rendering Good support.
Fidelity (high audio resolution) See AC-3.
Multiple channels See AC-3.
Support for user-defined sounds, samples, and patches Not applicable
Functionality beyond normal rendering Capable of including data that supports synchronization with video picture streams.

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension See note.  In general, not applicable; the encoded data will be in one of the "used by" formats listed in Relationships above.
Filename extension aes
Reported as an extension for raw data adhering to SMPTE ST 302 (Mapping of AES3 Data into an MPEG-2 Transport Stream) when saved as a file by Snell Wilcox devices.
Internet Media Type Not applicable.   

Notes Explanation of format description terms

General The main body of AES3 specifies signal transmission via a single shielded twisted wire pair. Annex D, however, discusses the carriage of AES3 signals on structured wiring, e.g., the "category 5" cables associated with computer network installations, a topic that receives extended treatment in AES47, which specifies the method of carrying multiple channels of audio in linear PCM or AES3 format across an asynchronous transfer mode (ATM) network. Elaborations on audio signal transfer are the topics of AES10-2003, AES Recommended Practice for Digital Audio Engineering -- Serial Multichannel Audio Digital Interface (MADI) (Revision of AES10-1991), and AES50-2005, AES standard for digital audio engineering -- High-resolution multi-channel audio interconnection.

Format specifications Explanation of format description terms

Useful references


Last Updated: 08/10/2021