Sustainability of Digital Formats
 Planning for Library of Congress Collections

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Identification and description

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

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

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; select "What I Need" from the site's home page.
Technical protection considerations	From the web site: "Audible created and employs a proprietary technology solution for distributing copyright-secure audio files that can be downloaded or streamed from audible.com. Audible's secure distribution system prevents a customer from passing along duplicate digital audio files to another listener." (This paragraph was found on the Audible.Com web site on May 12, 2004, by selecting "Help Center" from the home page, then selecting "Find an Answer," and clicking question 31: "Can I convert my books to MP3s?") Note that there is a provision to write content to audio CDs.

Quality and functionality factors

Sound
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

Tag	Value	Note
Filename extension	aa	Extension may be used for all Audible.Com formats [?]
Internet Media Type	audio/audible audio/x-pn-audibleaudio	From The File Extension Source. None found at http://www.iana.org/assignments/media-types/.
Magic numbers	None found

Notes

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.

History

Format specifications

• See Disclosure under Sustainability factors.

Useful references

URLs

• Audible.Com (http://www.audible.com).
• Discussion of formats (http://www.audible.com/formats). At Audible.Com Web site.
• VoiceAge (http://www.voiceage.com). Web site with information on ACELP speech encoding.
• IANA MIME Media Types (http://www.iana.org/assignments/media-types/).
• The File Extension Source (http://filext.com/).