Audiovisual Preservation Terminology
A glossary of common audiovisual preservation terminology.
Archival set for audiovisual collections: Set of like materials including a preservation copy, reference copy, intermediate copy, and replacement preservation copy.
Base: The material in film or magnetic tape that carries the recording layer; examples include polyester and acetate.
Compression format: The kind of compression that is used when storing reformatted audiovisual materials; e.g. mpeg 4.
Compression ratio: Expresses how much actual video information is stored versus how much is interpolated upon playback. The lower the ratio, the higher the quality of playback. However, less compression requires more storage capacity. 4:1 as a compression ratio and 4:2:2 as a sampling ratio are acceptable for preservation.
Conservation for audiovisual formats: Safely keeping the original audiovisual format and its hardware so that content can be retrieved.
Emulsion: Gelatin layer painted onto the film.
Generations of copies: Multiple copies of audiovisual materials are often found in archival collections. Many copies were made during the original production while others may come as the result of a preservation reformatting project. Copies that may be found in collections include:
Copies made during, or shortly after, original production:
Acquisition copy: Original recording made when the content was acquired.
Post production copy: Editing or mastering copy.
Distribution copy: Copy made from the edited master.
Archive copy: Copy generated later for preservation purposes.
Copies that are created for collections preservation:
Preservation copy: The best available copy that was accessioned into the collections; this copy should be as true to the original as possible. May also be called the preservation master.
Reference copy: Inexpensively made copy of the preservation material that is adequate for research room use; also called the access copy.
Intermediate copy: Copy made from the preservation copy that can be used as a duplicating master.
Replacement preservation copy: Copy made when the preservation copy begins to fail because the media itself is deteriorating or the technology that it was recorded on is no longer usable.
Lossless compression versus Lossy compression: A continuing discussion in the archives community is whether the digital signal created during preservation reformatting should be lossless or lossy. Lossless compression is any type of compression method that allows the materials to be uncompressed and retrieved without the loss of any data. However, lossy compression methods result in the loss of some data when the file is restored. While lossless compression is preferable because it means that there is no loss of information when the item is digitized, it is very difficult to find lossless compression in the current market.
Magnetic tape sound recording: One of two basic types of analog sound recordings; examples include cassettes and recordable tapes.
Mechanical sound recording: One of two basic types of analog sound recordings; played back with a stylus; examples include cylinders and discs.
Optical printer: A piece of equipment used in film preservation that prints original film images onto new film for preservation purposes.
Pulse Code Modulation (PCM): In sound preservation, it is the format in which a sound file is stored.
Preservation for audiovisual formats: Retaining the content of the original audiovisual materials so that it is safeguarded for future use.
Restoration for audiovisual formats: Rerecording the conserved item to make it more acceptable to modern ears and eyes.
Sticky shed syndrome: A preservation concern that occurs in magnetic tape when the binder fails and the surface of the tape becomes sticky and causes the tape to stick to itself.