Sustainability of Digital Formats: Planning for Library of Congress Collections

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Sound >> Preferences in Summary

This content was last reviewed and updated in 2009 and remains here for background information only. Beginning in 2015, the Library of Congress has published its format preferences as a Recommended Formats Statement, updated annually.

Device-independent digital sound recordings (waveform)

Note: This sub-category concerns device-independent digital audio. For preferences regarding sound in physical formats intended for consumer audio equipment, see the Phonorecords section (p. 3) of the Best Edition circular (7b) from the U.S. Copyright Office.

Fidelity characteristics (bitstream encoding) should be used as the primary consideration; choice of file formats as secondary.
Bitstream encoding for sound recordings (relates to fidelity)
• Higher sampling rate (usually expressed as kHz, e.g., 96kHz) preferred over lower sampling rate.
• 24-bit sample word-length preferred over shorter
• Linear PCM (uncompressed) preferred over compressed (lossy or lossless)
• Higher data rate (e.g. 128 kilobits per second) preferred over lower data rate for same compression scheme and sampling rate.
• AAC compression preferred over MPEG-layer 2 (MP3)
• Surround sound (5.1 or 7.1) encoding only necessary if essential to creator's intent. In other cases, uncompressed encoding in stereo is preferred

File type
• Not copy-protected rather than copy-protected
• Relatively complete descriptive and technical metadata rather than minimal
• Acceptable file formats for mono/stereo
  - WAVE_BWF_LPCM_1 or WAVE_BWF_LPCM_2, Broadcast WAVE Audio File Format, Versions 1 or 2, with LPCM Audio
  - WAVE_LPCM, WAVE Audio File Format with LPCM Audio
  - AIFF_LPCM, AIFF File Format with LPCM Audio
  - MP3_FF, MP3 File Format
  - AAC_ADIF, Advanced Audio Coding (MPEG-2), Audio Data Exchange Format
  - AAC_MP4, Advanced Audio Coding (MPEG-4), m4a File Format
  - QTA_AAC, QuickTime Audio, AAC Codec
  - WMA_WMA9_PRO, Windows Media Audio File with WMA9 Professional Codec
  - WMA_WMA9, Windows Media Audio File with WMA9 Codec
• Acceptable file formats for surround sound
  - AAC_ADIF, Advanced Audio Coding (MPEG-2), Audio Data Exchange Format
  - AAC_MP4, Advanced Audio Coding (MPEG-4), m4a File Format
  - QTA_AAC, QuickTime Audio, AAC Codec
  - WMA_WMA9_PRO, Windows Media Audio File with WMA9 Professional Codec

Note-based digital musical composition

• With associated sounds (either through General MIDI specifications or downloadable sounds) rather than without.
Bitstream encoding
MIDI_SD (sequence data) preferred over all other encodings. Digital compositions in other note-based formats should be submitted as audio waveform files. (Compilers seek advice re: preceding sentence.)
• General MIDI Level 1 preferred over General MIDI Level 2 for sequences (Level 2 may not be widely adopted); see MIDI_SD
DLS standardized downloadable sounds preferred to proprietary samples (compilers of this document seek advice about preference re: SoundFont sf2 format)
File type
XMF, eXtensible Music Format (if downloadable sounds are included)
SMF, Standard MIDI File
RMID, RIFF-based MIDI File

Recorded books

This sub-category consists of recorded books of the types likely to be added to the Library's collections. Generally speaking, these are commercially published works added to the holdings of the Motion Picture, Broadcasting, and Recorded Sound Division (M/B/RS); other recorded books are produced and archived by the National Library Service for the Blind and Physically Handicapped at the Library of Congress. Current guidelines in M/B/RS limit selection to works read by their authors and other readings of exceptional interest.

The baseline format preferences for recorded books are identical to those for device-independent digital sound recordings, as outlined above. The desired features for recorded books, however, include elements that are "beyond normal rendering" for other genres of sound. In a capable player, hardware or software, recorded book formats should support such end-user functions as bookmarking; automatic holding the last position (where play left off); display of time elapsed, time remaining, and the ability to go to a specified time; navigation to chapters, sections, or illustrations; display of descriptive information, e.g., title, name of author, name of narrator, name of chapter titles; and re-read capability (repeat last sentence or paragraph). Such support is offered by the DTB (Digital Talking Book) standard (ANSI/NISO Z39.86-2002). The DTB format can encompass a wide range of content elements, including marked-up text with no audio, audio and synchronized text, to audio with navigation control only. The latter structure, referred to as "audio with NCX only (Navigation Control)," is one form of DTB and ideal for stand-alone players. Similar navigation support is offered by formats like SMIL and will be offered by emerging standards from organizations like the Consumers Electronics Association and the Electronic Industries Alliance. The latter formats have not yet been documented at this Web site.

Last Updated: 05/ 3/2017