30
GUIDELINES FOR THE CREATION OF DIGITAL COLLECTIONS
Digitization Best Practices for Audio
This document sets forth guidelines for digitizing audio materials for CARLI Digital Collections.
The issues described concern sample rates, bit-depths, file formats, and equipment for the
analog-to-digital conversion of audio materials. Background information on digital audio and a
bibliography of selected additional readings are also provided.
This document was created by the CARLI Digital Collections Users’ Group (DCUG), standards
subcommittee.
For questions about this document, please contact CARLI at support@carli.illinois.edu
!"#$%&'()$*)"#+%,(-./"%0($"#1%!*$23".$4#1%5*/"%56'-($#%
There are several standards associated with digital audio. For commercial audio CDs,
manufacturers established the standard of 44.1 kHz sample rate with a 16-bit file, based on the
fact that the highest frequency recordable is one half of the sample rate. This means a 44.1 kHz
recording will support a top frequency of 22 kHz. Since most humans cannot hear sounds above
20 kHz, the music industry adopted the 44.1 kHz sampling rate for digital audio recordings
knowing that it would capture all human-audible sound.
Digital audio for use in libraries and cultural institutions—especially for preservation-quality
audio and audio digitized from an analog source—should use a higher sample rate and file bit-
depth. 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. A higher bit-depth allows more audio information to be
stored within the digital file, including support for a greater dynamic range. Based on these
reasons, the current standard for archival digitization of analog recordings requires the sample
rate to be 96 kHz with a 24-bit depth.
Master audio files should be saved uncompressed and in a widely-used file format, with
maximum likelihood of continued support. The WAV PCM file type, developed by Microsoft, is
readable by most audio software programs. Broadcast WAV (BWF) is an extension of the WAV
