MP3 [AUD-D2]

Record Type Audio Recordings
Expected Use Distribution Copy
Product Name MP3 [AUD-D2]
Product Purpose

This file can be used when speed of transfer rate or small file sizes are more important than quality.

Nature of Source Material

Any digital preservation or reproduction master file.

File Properties Data Format
Capture Information

Typical file size 128 Kbps: ~ .96 MB/minute or .057 GB/hour
256 Kbps: ~ 1.9 MB/ minute or .113 GB/hour

Possible File Derivatives

Derivatives are not made from this product category.

Other Information
  • This file is generally not retained.
  • 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.

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)
  • Duration
  • Average audio level
  • Peak levels
Logged data

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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