Audio Formats and Preservation
Sound Preservation and Different Audio Formats
The process of transferring of information to other sustainable and accessible formats is known as digitization, bearing the challenge of transcoding all media content, as well as related information such as metadata in a proper way. This means managing file based digital data in a sustainable way, so that access, documentation and authenticity can be enabled and preserved in the long term.
Sound Preservation
The Recorded Sound Collection at the Library of Congress is an Audio Visual Conservation in Culpeper, VA. Items date from the late 1880s to the present day and include everything from music to radio broadcasts to spoken word recordings to field recordings of traditional music, oral histories and actualities.
Each year, donations, acquisitions, and copyrights are added through formats from cylinders, 78, 45, or 33 1/3 RPM records, reel to reel audio tapes, 8 tracks, cassettes, CDs, or even wire.
The Recorded Sound Collection at the Library of Congress is an Audio Visual Conservation in Culpeper, VA. Items date from the late 1880s to the present day and include everything from music to radio broadcasts to spoken word recordings to field recordings of traditional music, oral histories and actualities.
Each year, donations, acquisitions, and copyrights are added through formats from cylinders, 78, 45, or 33 1/3 RPM records, reel to reel audio tapes, 8 tracks, cassettes, CDs, or even wire.
For shattered cylinder, if the Library inherits all its pieces, some formats more stable than others, using a variety of means, and carefully glue it back together. Worn out or heavily worn 78 platters can be played for maximum sound quality by experimenting with stylus sizes. Tapes affected with sticky shed syndrome, a wearing away of the glue that holds magnetic particles to tape, can be baked at a low temperature, a process that reactivates their magnetic bindings. Almost all items require some degree of cleaning.
Deterioration of Sound
Because recorded sound is so pervasive in modern life, we may not realize how susceptible it is to deterioration and loss. Since the end of the nineteenth century, technological innovations have enabled people to record sound with greater ease and fidelity. Experts have experimented with and improved techniques of recording and playback, and developed new audio media, or carriers. For analog sound carriers, levels of risk vary according to their physical composition, storage conditions over time, and access to playback equipment and the knowledge to use it. The availability of proper storage space, functioning playback equipment, and expertise in working with obsolete formats diminishes.
From the 1950s to the 1980s, open reel quarter inch tape was the preferred medium of professionals. Never perceived as being permanent, tape was considered to be, and probably was at the time, the best affordable medium available for long term preservation. All the while, it was hoped that modern science and technology would develop a permanent medium. That never occurred, and worse, by the early 1990s, many preservation master tapes were found to be unplayable because they suffered from sticky shed syndrome. In the late 1980s and early 1990s, both digital audio tape, DAT, and the recordable compact disc, CD-R, were thought to have promise as preservation media, but they have proved to be unreliable for archival purposes. As a result, the original recordings that were reformatted for preservation have often outlasted the reformatted versions.
Deterioration of Sound Formats
- Brown wax cylinder - Fingerprints on playback surfaces leave behind organic compounds that not only attract dust and dirt, but also encourage microorganism damage. Wax cylinders are also fragile and can be easily broken through improper handling.
- Shellac 78 RPM Record - Shellac discs are a robust and relatively stable format. Shellac discs become more brittle over time, particularly if stored without sufficient temperature and humidity controls. The organic cellulosic material present in most discs is susceptible to fungal growth, especially if conditions are humid or if the discs are exposed to water and not quickly dried. Exposure to water can also cause networks of fine cracks on the playback surface, a condition referred to as crazing.
- Vinyl Records - Vinyl records are the most stable physical sound recording format developed to date, they can last 100 years in a controlled environment. However, heat and ultraviolet radiation both degrade the polymer. Vinyl softens and flows when exposed to excessive heat, which deforms the grooves. Excessive heat, ultraviolet radiation, and humidity accelerate the degradation and deplete the available stabilizers. Dust and foreign matter, such as oils from fingers, can cause distortion and surface noise in playback, these deposits can promote fungal growth and damage the playback surface. Water can combine with the offgassing of hydrogen chloride to form hydrochloric acid in excessively hot conditions. Heat and pressure can also cause the record to warp, which can adversely affect playback. Vinyl records are relatively soft compared with shellac records, and they are susceptible to mechanical damage, such as scratches. Consequently, they require much lighter downforce from the tonearm on a playback device than do shellac records. Because polystyrene is softer than PVC, these records are also more susceptible to mechanical damage caused by the playback needle gouging the surface as it plays.
- Wire Recordings - Early non stainless steel wires may be susceptible to corrosion and rust. The most serious deterioration is caused by wire breaking and becoming tangled, as the wire travels through the playback mechanisms at a high speed. Splices or repairs were achieved by tying the wire in a standard square knot and pulling it tight. Some early practitioners bonded wire ends together with a lit cigarette.
- Cartridges, 8 tracks, Compact cassette, and Microcassette - The inevitable loss of tape lubrication within cartridges can cause the tape to wind improperly or stick together when unwound during playback. The pinch roller in some cartridges was made of improperly cured rubber, which can allow the roller to become dented or misshapen, particularly if exposed to excessive heat. Both of these factors contribute to a risk of tape snarls and catastrophic malfunction. The portable design of cartridge and cassette tapes encourages listening in all environments, and this makes them especially susceptible to binder hydrolysis. High capacity tapes use very thin polyester tape and are at a high risk of deformation, especially when stored in hot and humid environments.
- Digital Audio Tape (DAT) - The pure iron pigments used in the magnetic layer of DATs are susceptible to oxidation, rust. Binder hydrolysis in the polyester urethane binder has proven to be a prevalent issue with many DATs, causing complete loss of information. The high speeds produced by the rotating heads passing by the moving tape exacerbate damage to the information layer. After the error threshold is crossed, the information is irretrievable. These factors combine to make DATs a very high risk format.
- Pressed Compact Disc - Both polycarbonate layers are susceptible to damage. Scratches and abrasions to the bottom layer can cause read errors and, if severe enough, can prevent successful playback. The top layer, where the information is actually stored, can be damaged by acidic inks from pens or markers used to label a CD, or from dyes and adhesives used to decorate and label the disc. Accelerated testing conducted at the Library of Congress has indicated that the reflective metallic layer can delaminate from the polycarbonate plastic when a disc cycles repeatedly through heat and cold.
Sound Archives
The Library of Congress numbers in excess of three million items and adds a further 75,000 sound items each year.
The National Archives multimedia collections include nearly 300,000 reels of motion picture film and more than 200,000 sound and video recordings.
The Association for Recorded Sound Collections, Inc. is a nonprofit organization dedicated to the preservation and study of sound recordings in all formats, consisting of more than 1000 knowledgeable members who really care about sound recordings.
The Audio Engineering Society was founded in the USA in 1948. An international organization that unites audio engineers, creative artists, scientists and students with over 12,000 members.
Additional information about preserving and archiving sound:
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