Preservation

Audio Maximum Capture [AUD-P1]

Record Type Audio Recordings
Expected Use Preservation Master
Product Name Audio Maximum Capture [AUD-P1]
Product Purpose

The purpose of this product is to mitigate the risk of loss of information. This file is at an appropriate information capture level to substitute for the original record if the original record copy is no longer viable.

Nature of Source Material

Analog recordings with a wide dynamic range, of high content value and/or of a complex nature and material of limited quantity and high cultural/historical significance where there is a need to ensure that all significant auditory information is carried forward. Examples include recordings where unique music is the primary focus and oral histories/interviews where background noise or other ambient noise is vital to capture.

File Properties Data Format
  • Broadcast WAV (.wav) as defined by The European Broadcasting Union in document Tech 3285
  • Uncompressed
  • Version: 1
Capture Information
  • Encoded to Linear Pulse Code Modulation (LPCM)
  • Sampling frequency: 96 kHz
  • Bit depth: 24
  • Sound field: as in original recording
  • Byte order: Little endian

Typical file size Mono: ~ 17.28 MB/minute or 1 GB/hour
Stereo: ~ 134.5 MB/minute or 2 GB/hour

Possible File Derivatives

This master file can be used to create any preservation, reproduction or distribution file of equal or lesser capture quality.

Other Information

Using these capture parameters, the resulting file sizes are generally three times larger than, for example, files of Audio Median Capture [AUD-R1].

This file will not be altered in any capacity except for level adjustment to be employed at the initial capture stage.

Quality Control Quality Control for Digital Audio Files

Using automated batch-processing software tools, test plans are developed for each format and/or each appropriate project. The test plan allows for some characteristics to be evaluated on an actionable basis (warning, fail or pass depending on the defined parameters). Others are logged for internal use but are not actionable as a warning, pass or fail. Aim points for these benchmarks are evaluated against NARA's product specifications as well as NARA defined aim points which may change depending on specific project goals. The following represents the quality test plan technical characteristics for WAV and MP3 products.

Metadata
Embedded metadata compliance: NARA follows the FADGI Embedded Metadata in Broadcast WAVE File Guidelines. NARA does not embed metadata into MP3 files.
Technical metadata: NARA is finalizing a technical metadata schema for audio files based on the same structure as its reVTMD schema for video technical metadata.

Item Level Evaluation: Automated Quality Analysis

Fixity: NARA is evaluating workflows to create and validate checksums for each digital file.

Terms used in the QC protocols are defined in the Glossary of Terms.

Technical Characteristic Warning/Pass/Fail or Logged Data
  • Sampling Frequency (Hz)
  • Audio Channels (Number)
  • Bits per sample (Number)
Warning/Pass/Fail
  • Duration
  • Average audio level
  • Peak levels
Logged data
Rationale

The digital preservation masters products produced by the Audio Preservation Lab are in line with published guidelines and best practices including the IASA TC-04: Guidelines for the Production and Preservation of Digital Audio Objects and ARSC Preservation of Archival Sound Recordings.

Reproduction masters are also BWF files but at the minimum CD Quality specification.

Distribution copies include a CD output option as well as an online delivery option.

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