File formats for oral history

[Jonathan Draper]

A common question is what file format should I use to record oral history interviews which are designed to be kept permanently. The general advice (by organizations such as IASA) is record as uncompressed wave files (.wav) with a sample frequency of 96 kHz and bit depth of 24. Using these settings creates large files; one hour of a stereo recording will be just over 1 GB. However, such files contain a lot of digital information, which means, when played back, they are a very accurate reproduction of the audio recorded. If you are unable to record with these setting, the minimum sample frequency and bit depth you use should be 44.1 kHz and 16 respectively. 

Any editing of the master file should be done to the wave file, e.g. top and tailing the recording. This is the file which should be archived at institutions such as the Norfolk Record Office. You can convert these high quality wave files to other file formats for access and other dissemination purposes. The most common file type for access is MP3. This is a compressed lossy file type. What that means is, in order to make the file as portable as possible, the conversion process removes a lot of the digital data used to describe the audio. This data is lost forever in the conversion process but it does make the file, about the tenth the size of the original wave file. Ideal for putting on your phone. It is usually difficult to tell the difference between a good quality MP3 file and the wave file, but for archival purposes, it is useful to have as much audio data as possible.

There is no point in converting an MP3 back to a wave file. Though you are making a bigger file, you are not actually creating any meaningful data.

In conclusion, if all we have is an MP3 file, then archive repositories can preserve it, but, speaking for the NRO, our preference would be an uncompressed wave file. If you are planning an oral history project with the intention of depositing files with an institution, contact that institution during your planning stage to find out what they would like.

Best wishes,

Jonathan