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The Recording, Retention And Playback Of Sound
The Degradation Mechanisms Of Sound Recording
Preservation Of Sound Recordings
Conclusion And Bibliography
Consultation And References
PRESERVATION OF SOUND RECORDINGS
A good definition of preservation put forward by the International Institute for Conservation--Canadian Group and the Canadian Association of Professional Conservators is that preservation encompasses "all actions taken to retard deterioration of, or to prevent damage to, cultural property. Preservation involves controlling the environment and conditions of use, and may include treatment in order to maintain a cultural property, as nearly as possible, in an unchanging state." (see reference 11)
There are essentially only three concerns to consider when handling and storing sound recordings:
1) that they be kept free of any foreign matter
1. FOREIGN MATTER DEPOSITS
Dirt can be classified into two categories:
(1) Foreign matter deposits which are not part of the
original object, such as grease from fingerprints, soot, stains, adhesives, etc. and
Dust is commonly a mixture of fragments of human skin, minute particles of mineral or plant material, textile fibres, industrial smoke, grease from fingerprints, and other organic and inorganic materials. There are often salts such as sodium chloride (carried in from sea spray or on skin fragments), and sharp gritty silica crystals. In this chemical mixture are the spore of countless moulds, fungi and micro-organisms which live on the organic material in the dust (fingerprints, for example, serve as good culture media). Much of the dirt is hygroscopic (water-attracting) and this tendency can encourage the growth of moulds, as well as increase the corrosiveness of salts, hydrolysis and the release of acids. (see reference 13)
Dust (including fingerprints) will negatively affect sound recording preservation in a number of ways:
Dust is abrasive, and combined with the pressure exerted on the groove walls by the stylus, can permanently etch the walls worse, dust can also be imbedded permanently into thermoplastic substances. Only a small point of the stylus is actually making contact with the groove walls. One and a half grams of stylus pressure on such a minute surface translates to several tons of pressure per square inch. The resulting drag generates enough heat that the plastic partially melts (though not enough to deform), causing a microscopic flow around the stylus into which dust can be embedded permanently.
Dust attracts and traps moisture and will precipitate hydrolysis, a common and serious cause of long-term magnetic tape degradation. Also, dust may cause permanent damage to the tape when the abrasiveness of the dust along with the pressure exerted between the tape surface and the tape recorder heads will scratch the oxide layer and the tape recorder heads.
Since there is no physical contact at playback, there is virtually no chance of physical damage occurring during playback due to dust deposits. Nevertheless, dust will impede proper playback by obstructing the reading of the information, while it may also affect the long-term preservation. At present, the precise, long-term degradation mechanisms for the CD are still unknown, but physical damage will occur owing to the scratching of the protective layer.
TO MINIMIZE FOREIGN MATTER DEPOSITS:GENERAL:
CLEANING (see reference 14)Since dust is usually held in place by electrostatic attraction, dry wiping on its own does not work effectively. The added friction created by the duster will cause the dust to jump back to the charged surface.
Distilled water is used for cleaning records and CDs for many reasons. Its precise chemical makeup is known, it will not leave any residue behind, is safe to use, and is inexpensive. Water disperses static charges and counteracts the increase in conductivity from the pick-up of salt deposits from finger prints. However, water alone cannot dissolve grease, thus surfactants are used as additives to enable water to be a grease solvent. Surfactants break grease surface bonds and allow water to penetrate grease solids, causing swelling and then random dispersion.
2. SURFACE DEFORMATIONS
Since the surface of a sound recording is the information carrier, it is critical that the surface be well cared for. Physical deformations such as warping of discs, stretching of tape or shock from dropping them, will directly affect sound information integrity. One must develop a respect for the integrity of the artifact.
TO MINIMIZE DEFORMATIONS
A proper environment for the storage of sound recording is essential to retard degradation mechanisms. Elevated temperature and humidity can affect certain chemical properties of the plastics that make up recording media and can also create an environment that encourages the growth of fungus. Wide or rapid fluctuations of the environment are equally detrimental to the long term preservation of sound artifacts.
Shrinkage of the lacquer coating due to the loss of plasticizer is the primary destructive force of these discs. Excess moisture will accelerate plasticizer loss. Acetate discs decompose continuously, and over time react with water vapour or oxygen to produce acids that in turn act as catalysts for several other chemical reactions. One of these is the release of palmitic acid, a white waxy substance. Acetate discs are very susceptible to fungus growth. Excess heat will probably accelerate the loss of the coating adhesion.
Vulcanite discs are adversely affected by elevated levels of light, heat and humidity. In response to light and heat, Vulcanite loses sulfur. Light induces oxidation and form oxides of sulfur and sulfuric acid in the presence of humidity. The acidity builds up to a level at which the degrading material is attacked and eventually decomposed. (see reference 15)
High humidity levels accelerate the embrittlement of shellac discs. This embrittlement causes a fine powder to be shed from the disc after each playback, effectively scraping away groove information. The severity of the embrittlement is unpredictable, due to the wide combinations and variety of materials (and of material quality) that were used during their production. The average shellac content in a shellac disc is approximately 15 % with the remaining 85% composed of aggregates. Organic materials in the aggregates are susceptible to fungus attack, while shellac itself is said to be fungus-resistant.
Vinyl discs are adversely affected by ultraviolet light and thermal cycling (heat fluctuation). The consequence of thermal cycling is that each cycle of temperature results in a small irreversible deformation, and these deformations are cumulative. (see reference 16) Vinyl discs are resistant to fungal growth and are unaffected by high humidity levels.
Hydrolysis is the chemical reaction whereby the binder resin "consumes" water drawn from humidity in the air to liberate carboxylic acid and alcohol. Hydrolysis in magnetic tape results in the binder shedding a gummy and tacky material which causes tape layers to stick together and inhibits playback when it is deposited onto the tape recorder heads. Hydrolysis also causes a weakening in the bond holding the binder to the backing, which results in shedding or possible detachment.
Cellulose acetate backed tapes are very susceptible to linear expansion in humid and/or warm conditions. Because of the different properties of the binder and the base, the absorption of humidity and heat result in tape curling and edge fluttering. Repeated dimensional changes due to environmental fluctuations grossly affect winding tension (hence the need for periodic rewinding) and can promote binder fatigue, cracking, and finally, the irreversible loss of sound information (known as catastrophic failure).
Tape binder is somewhat susceptible to fungi growth though less so with modern tapes as fungicides are presently incorporated into the binder. The process of the break-down of acetate backed tape is exhibited by the release of acetic acid. It is accelerated by the presence of moisture and iron ferromagnetic particles in the tapes. When the acetate is degrading --giving off acetic acid odour-- it starts to take up more moisture. The process of self-destruction is autocatalytic.
The compact disc is a laminate of 4 different materials. The bottom of the disc is made of polycarbonate onto which the pits containing the digitized sound information are stamped. A thin layer of aluminum is then applied, covering the pits. A thin lacquer coating (which becomes the top of the disc) is then applied to cover the aluminum layer, and finally the ink for the labeling.
As with any laminated products, one must wonder how the aging characteristics of each material will interact with, and affect adjacent layers.
PROPER STORAGE ENVIRONMENT
Over the past century, recorded sound has become an intrinsic part of our culture. Upon hearing an early sound recording device in 1888, Sir Arthur Sullivan stated that he was "astonished and somewhat terrified at the result of this evening's experiments--astonished at the wonderful power you have developed, and terrified at the thought that so much hideous and bad music may be put on record forever." (see reference 18) Unfortunately, sound recordings are not "forever". These are ephemeral documents, both in their physical composition and consequently in the means by which the sound is ultimately retained. They can have their life span shortened considerably by both internal and external forces. By undertaking certain precautionary measures, custodians of the heritage of sound can lengthen considerably their collection's life span thus preserving a rich, invaluable world of sound.
Archiving the Audiovisual Heritage, a Joint Technical Symposium. -- FIAF (Fédération International des Archives du Film), FIAT (Fédération International des Archives de Télévision), IASA (International Association of Sound Archives). -- Berlin: Stiftung Deutsche Kinemathek, 1988.
Association for Recorded Sound Collections, Associated Audio Archives Committee. -- Final Performance Report: Audio Preservation: A Planning Study. -- Silver Spring, Maryland: Association for Recorded Sound Collections, 1987.
Borwick, John -- Sound Recording Practice, Third Edition. -- Oxford University Press, 1989.
Bradshaw, R.; Bhushan, B.,; Kalthoff, C.; Warne, M. -- "Chemical and Mechanical Performance of Flexible Magnetic Tape Containing Chromium Dioxide". -- IBM Journal of Research Development. Vol. 30, No. 2, March 1986. pp. 203-216.
Brown, Daniel W.; Lowry, Robert E.; Smith, Leslie E. -- Prediction of the Long Term Stability of Polyester-Based Recording Media. NBSIR 83-2750. --US Department of Commerce, August 1983.
Brown, Daniel W.; Lowry, Robert E.; Smith, Leslie E. -- Prediction of the Long Term Stability of Polyester-Based Recording Media. NBSIR 82-2530. --US Department of Commerce, June 1982.
Committee on Preservation of Historical Records, et al. -- "Magnetic Recording Media" in Preservation of Historical Records. -- Washington, D.C.: National Academy Press, 1986, pp. 61-69.
Cuddihy, E.F. -- "Aging of Magnetic Recording Tape". -- IEEE Transaction on Magnetics. Vol. 16, No. 4, July 1980. -- pp. 558-568.
Cuddihy, E.F. -- "Stability and Preservation of Magnetic Tape". -- Proceedings of the International Symposium: Conservation in Archives. --Conseil international des archives 1989, pp. 191-206
Fontaine, Jean-Marc. -- "Conservation des Enregistrements Sonores sur Bandes Magnétiques, Étude bibliographique". -- Analyse et Conservation des documents graphiques et sonores. -- Paris, France: Éditions du centre de la recherche scientifique. 1984.
Fontaine, Jean-Marc. -- Degradation de L'Enregistrement Magnetique Audio/Degradation of Magnetic Audio Recording.-- 1987. (unpublished) [An English translation, Degradation of Magnetic Audio Recording, was prepared by the National Library of Canada.]
"The Handling & Storage of Magnetic Tape" -- Sound Talk. Volume III No. 1, 3M, 1970.
Jorgensen, Finn -- The Complete Handbook of Magnetic Recording: 3rd Edition--Blue Ridge Summit, PA: Tab Professional and Reference Books-- 1988.
Kalil, F., (Ed.) -- Magnetic Tape Recording for the Eighties: NASA Reference Publication 1075. -- Tape Head Interface Committee, 1982.
Lehn, Anna -- Appendix IV "Recommended Procedures for Handling Audiovisual Material" -- Final Report: Working Group on the Preservation of Recorded Sound Recordings. -- Ottawa: National Library of Canada, 1990. [Unpublished].
Morgan, John -- Conservation of Plastics: An introduction to their history, manufacture, deterioration, identification and care. London, England: Plastics Historical Society; The Conservation Unit, Museums & Galleries Commission, 1991.
Moncrieff, Anne; Weaver, Graham -- Science for Conservators: Cleaning. --London: Crafts Council, 1983.
Pickett, A.G.; Lemcoe, M.M. -- Preservation and Storage of Sound Recordings. -- Washington, D.C.: Library of Congress, 1959.
Pohlmann, Ken C. -- The Compact Disc: A Handbook of Theory and Use. --Madison, Wisconsin: A-R Editions Inc, 1989.
Preservation and Restoration of Moving Images and Sound -- FIAF (Fédération International des Archives du Film), 1986.
Smith, Leslie E.; Brown, Daniel W.; Lowry, Robert E. -- Prediction of the Long Term Stability of Polyester-Based Recording Media. NBSIR 86-3474. --US Department of Commerce, June 1986.
Storage of Magnetic Tapes and Cinefilms -- European Broadcasting Union, Technical Centre, Brussels, 1974.
Wheeler, Jim -- Increasing the Life of Your Audio Tapes. -- Ampex Corporation, 1987.
Woram, John M. -- The Recording Studio Handbook.-- Plainview, New York: Sagamore Publishing Company Inc., 1980.
Bob Barclay and Scott Williams, Canadian Conservation Institute;
REFERENCES (cited within this text)
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