3. The instability and vulnerability of audiovisual carriers
For traditional paper and film-based documents, the long-term preservation of the original carrier is, with a few exceptions, generally feasible. Printed or handwritten text as well as film-based documents may remain fully human-readable even when damaged, whereas the continuous, time-based nature of audiovisual documents means that any compromise in the integrity of the document will result in the loss of information.
In addition, audiovisual carriers are generally more vulnerable than conventional text documents to damage caused by poor handling, poorly maintained equipment or by poor storage. Many audiovisual carriers, especially magnetic recordings, laminated instantaneous discs, and nitrate film, have relatively short life expectancies due to their physical composition. Whereas script has a high level of redundancy, which keeps text documents often readable even in damaged condition, audiovisual documents are representations of physical facts or processes: their redundancy is low, as each detail is potential information that must be preserved, which calls for highest possible integrity standards.
These factors have led to the development of a wide range of best practices for the storage and cleaning of carriers, and for the transfer of content to digital file-based formats. Passive preservation is discussed in detail in IASA-TC 05: Handling and Storage of Audio and Video Carriers.
Due to the high density of information, digital carriers are generally more vulnerable to loss of information through damage than analogue carriers. Life expectancy concerns particularly arise in the case of the storage media used in most computer-based storage and data management systems. Their useful life is generally short—from three to ten years—due to a combination of system and storage-media-format obsolescence, as well as risks related to the high density of the data carried by data-storage media.
Comment:
High data density and the risk of data loss is a particular concern for digital video carriers containing Metal Evaporated (ME) tape.
The level of risk to a carrier will depend in part upon its vulnerability to decay or damage. It also depends upon the storage conditions under which the carrier has been held, upon the quality and maintenance of replay equipment, and upon the professional skills of the operator.
Digital carriers will fail without warning, and without the audible or visible clues of gradual degradation that analogue carriers present. Damage to a digital carrier’s logical structure may also render the content inaccessible.
