Audio

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Preservation Format

LPCM/WAVE

Access Format

MP3

Normalization tool

FFmpeg

Comments

• For the preservation master, audio files are normalized to WAVE LPCM with a bit depth of 16 bits per sample. The sampling frequency of the original file is maintained. If the ingested file has a bit depth of greater than 16, normalization will be adjusted to use the higher bit depth.
  • Library of Congress considers WAVE LPCM as the "preferred format for sound recordings." Library of Congress Sustainability of Digital Formats: WAVE Audio File Format with LPCM audio
  • Florida Digital Archive normalizes audio streams contained in WAVE files to uncompressed PCM(LPCM) with a bit depth of 16 bits per sample. See Preservation action plans: WAVE.
  • According to Guidelines for the Creation of Digital Collections: Digitization Best Practices for Audio, Consortium of Academic and Research Libraries in Illinois, 2009, WAVE LPCM with with a bit-depth of 16 bits and a sampling freqency of 44100 HZ is the minimum standard for a preservation format (p. 2). Higher bit depth and sampling frequencies may be desirable: "Several specific reasons for richer files include: the accurate capture of noise like clicks, pop, and other inaudible information that resides in frequencies higher than 44.1 kHz; desire to communicate inaudible harmonic information that impact perception of sound; ability to record and provide content that, although not necessarily heard, helps listeners understand and hear better space, depth, and instrument location in stereo and surround sound recordings; and to accommodate future user applications." (p.1)
• For the access copy, audio files are normalized to MP3 using a bit-rate of 192 kbp/s.
  • According to Guidelines for the Creation of Digital Collections: Digitization Best Practices for Audio, Consortium of Academic and Research Libraries in Illinois, 2009,"Access copies for audio files may be saved in compressed formats that allow for quicker transfer or streaming via the Internet. The MP3 format is widely-supported, is playable on nearly all handheld devices, and is commonly used for web delivery. MP3 is the preferred format. MP3 files saved at 192 Kbps (the bit-rate) are recommended for good quality compressed audio." (p.2)