Preservation

Audio Median Capture [AUD-R1]

Record Type Audio Recordings
Expected Use Reproduction Master
Product Name Audio Median Capture [AUD-R1]
Product Purpose

The purpose of this product is to respond to reference and reproduction requests.

Nature of Source Material

Any digital master audio file not at risk due to deterioration or obsolescence.

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: 44.1 kHz
  • Bit depth: 16
  • Sound field: as in digital master source file
  • Byte order: Little endian

Typical file size Mono: ~ 5.3 MB/minute or .317 GB/hour
Stereo: ~ 10.5 MB/minute or .635 GB/hour

Possible File Derivatives

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

Other Information
  • This product meets the minimum quality defined for CD output and can be used as either a Reproduction Master file or Distribution file.
  • If used as a Reproduction Master file, the file is permanently retained; if used as an Distribution file, the file is usually not retained after burning to a CD-R as a data file.
  • Audio levels may be adjusted as appropriate during the initial capture process. Reproduction and distribution files may have additional improvements such as the application of an EQ curve for grooved discs.
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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