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.
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.
- 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.
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