Sustainability of Digital Formats: Planning for Library of Congress Collections

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Audible.Com File Format

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Format Description Properties Explanation of format description terms

Identification and description Explanation of format description terms

Full name Audible.Com File Format
Description File format for sound that wraps various audio bitstreams. Audible.Com is a seller of recorded sound products, ranging from talking books to archived radio programs, e.g., Car Talk. See Notes for more information.
Production phase Used for final-state, end-user delivery.
Relationship to other formats
    Has subtype AudCom_MP3, Audible.Com MP3
    Has subtype Audible.Com HAC (hearing aid compatibility) format, not documented here
    Has subtype Audible.Com ACELP speech encoding, not documented here
    Has subtype Audible.Com files containing other sound encodings not documented here
    May contain MP3_ENC, MP3 Encoding
    May contain SONY HAC (hearing aid compatibility) encoding, not documented here
    May contain VoiceAge ACELP speech encoding, not documented here
    May contain Other sound encodings, not documented here

Local use Explanation of format description terms

LC experience or existing holdings None
LC preference General preference for preservation recorded sound is WAVE_LCPM. For compressed audio, MP3_FF is preferred to AudCom_MP3; within the Audible.Com family, however, AudCom_MP3 is preferred to other encodings.

Sustainability factors Explanation of format description terms

Disclosure Not documented. Proprietary format of Audible.Com
    Documentation Compilers of this document were unable to locate specifications for the wrapper format.
Adoption Not known to the compilers of this document. Audible.Com is a visible player in the downloadable sound marketplace and appears to be actively distributing product.
    Licensing and patents Not known to the compilers of this document.
Transparency Unknown; see note on technological protection below.
Self-documentation Not known to the compilers of this document. Evidence at the web site suggests that the files carry some descriptive ("bibliographic") information, e.g., author, title, and duration.
External dependencies Files can be played only on certain players. As of September 2015, these include applications for personal computers and many mobile devices. See Audible's Help Center and Device Center.
Technical protection considerations

From the Audible Web site consulted in September 2015: "We apologize for the inconvenience, but Audible audio files cannot be converted into MP3 or any other file format. The reason for this is because we utilize security technologies to protect the intellectual property rights of our content providers and authors." Slightly different wording was provided at the site in 2004: "Audible created and employs a proprietary technology solution for distributing copyright-secure audio files that can be downloaded or streamed from Audible's secure distribution system prevents a customer from passing along duplicate digital audio files to another listener." Note that there is a provision for subscribers to write/burn audio files in Audible format to CDs playable in regular CD players using iTunes [see help on listening to Audible content in a car]. Burning to CD is only allowed once for an audio book.

Quality and functionality factors Explanation of format description terms

Normal rendering Good support.
Fidelity (high audio resolution) Moderate to good, depending upon encoding selected; the web site compares the formats in terms of fidelity and other factors.
Multiple channels Apparently not
Support for user-defined sounds, samples, and patches Not supported
Functionality beyond normal rendering None described

File type signifiers and format identifiers Explanation of format description terms

Tag Value Note
Filename extension aa
Extension may be used for all Audible.Com formats [?]
Internet Media Type audio/audible
From The File Extension Source. None found at
Magic numbers Not found.  Comments welcome.   

Notes Explanation of format description terms

General The formats used by the company range from highly compressed speech encodings to less compressed MP3_ENC (MP3 encoding). The site states, "The more information, or bits, the fuller and richer the sound." Programs that feature music are not offered in the most compressed formats. More information on the Audible.Com formats page. Another page at the site reports that "Audible's preferred speech codec is licensed from VoiceAge Corporation," presumably the ACELP (Algebraic Code Excited Linear Prediction) encoding described by VoiceAge.

Format specifications Explanation of format description terms

Useful references


Last Updated: 03/16/2020