Digital audio technical metadata

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Published date: 
Wednesday, October 19, 2016 - 1:15pm

Hello again! I thought I would share some of the important metadata work that I am doing here at KBOO.

Here's a little screencast sneak peek at some of the metadata entry for KBOO radio audio content: http://bit.ly/2eH4IU5

KBOO has digital audio files: content digitally captured from physical formats like open reel audio, cassettes, or minidiscs and content that is born-digital like the current broadcast audio files. Digital audiovisual technical metadata enables us to ensure that the file has been digitized at the level of best practices, and matches the source content. Examples of technical metadata fields for audio include channel configuration, file encoding, sample rate, bit depth, and audio codec.

The free software MediaInfo is available for Mac, Windows, and other operating systems. MediaInfo is a convenient unified display of the most relevant technical and tag data for video and audio files. Digital files hold information about themselves in the file. MediaInfo allows drag and drop of files into the graphical user interface, and copy/paste of metadata. MediaInfo also will detect the capture software used to create the digital file, and other details necessary if audio professionals or archivists need to troubleshoot files.

You'll notice our archival filenaming convention:

kboo_[inventor unique identifier]_[date associated with the file]_[optional human readable title].wav

When a group of files follows the same filenaming convention, it infers additional information about the files. In this case, it is important for each file to match back to a unique item in our archive.

I create md5 checksum strings for each file so that the fixity of the file can be administered over time. Fixity is like checking a fingerprint of your file. Digital files have preservation risks just like physical materials. When a digital file is created, it is necessary to ensure that the file is unchanging, and to provide a method of retrieval of a trusted file (i.e. from a backup) that represents the file that entered the digital repository. 

A few notes:

In-house digitization of minidiscs occured in Fall 2015 and the sample rate/bit depth chosen was 44.1kHz at 16 bits. The current best practice for audio preservation quality files is to digitize at 96kHz at 24 bits. 44.1kHz is CD-quality recording and just covers the range of human hearing. 48kHz at 24 bits is the common digitization standard for audio streams in video files.

Source formats like minidiscs often have their own channel configuration. It is important that the digitization settings match this, i.e. 1 channel to 1 channel, 2 channels to 2 channels.

Audio preservation file formats should always be lossless, meaning the file is not compressed, therefore not removing any data.

Many more metadata fields are represented in our master data sheet to describe the content, including descriptive metadata. Descriptive metadata is usually the kind of information users are most interested in, i.e. the keywords you search for to bring up search results, the title, description, and host names.