Sound Recordings
Gramophone or Phonograph Records
Most gramophone or phonograph record disks in library and archive collections are made of polyvinyl-chloride or shellac. Gramophone records have some raw materials in common with books and manuscripts: they use lampblack, and ground wood is often used as a filler for shellac disks. Disks generally are in three sizes: 12 inch (usually long-play records at 33 1/3 revolutions per minute, or rpm), 78 rpm records, and 7-inch (usually 45 rpm).
Record disks are usually housed in paper sleeves and labeled on paper. Thus the commercial packaging is a vital part of the disk provenance. Appropriate packaging and housing for disks are important, because the sound quality is affected by dust and mold gathering in the grooves. A dust-free environment is desirable for the storage and use of disks. If the storage area cannot be maintained, a tightly closed steel cabinet can reduce dust contamination.
Another major concern is the warping that can result from the sagging of disks stored vertically. This can also adversely affect the sound quality. Disks can be stored vertically but in a fashion that prevents them from slumping and keeps them perfectly upright. Vinyl records have a fairly stable shelf life under the proper conditions, but due to rapid, increasing risk of playback machinery obsolescence, digital migration is recommended.
Magnetic Audiotape
Early magnetic audiotape from the 1950s and 1960s utilized an acetate film base, which can deteriorate relatively quickly. Modern tape uses a polyethylene terephthalate (PET) film base with an iron-oxide coating bound with polyurethane. Chromium-dioxide has been used on some tapes with a PET coating.
Most forms of audiotape should be considered chemically unstable if not kept at temperatures near 18 to 21° degrees Celsius and a relative humidity (RH) of 40 – 50% percent. Variations in temperature and humidity can cause tape problems, including binder breakdown or hydrolysis and expanding and contracting of tape.
Tape tension is another important consideration in maintaining proper storage. Tape packs are wound under a considerable amount of tension. This is necessary to maintain the shape of the tape pack. A reel of tape can be permanently damaged if the tape pack tension is too high or too low. If the tension is too high, the tape backing can stretch. If the tension gets too low, tape layers can slip past each other, resulting in pack slip, cinching, or popped strands on playback. Relaxation of the tape backing can also occur if the tape pack tension is not properly maintained. Relaxation, stretching, and deformation of the tape backing can cause sound distortion on an audiotape. Every time a tape pack is heated or cooled, the tape pack tension will increase or decrease, respectively. The best way to reduce the degree of tape backing distortion is to store magnetic media in an environment that does not vary much in temperature or humidity.
Thin tapes, typically used in audiocassettes, are inappropriate for archival retention; the thinner tape allows stretching and “print-through,” in which sounds from both sides can sometimes be heard. As with most forms of sound recordings, maintenance of playback equipment is of prime importance and involves calibration and weighted testing periodically to conform with international preservation standards.
Magnetic tape in general is ultimately considered a high-risk format and should be migrated as soon as possible, preferably to a redundant, digital format.
Relevant readings
St-Laurent, Giles. 1996. The Care and Handling of Recorded Sound Materials. [http://palimpsest.stanford.edu/byauth/st-laurent/care.html].
Van Bogart, John. 1995. Magnetic Tape Storage and Handling: A Guide for Libraries and Archives. Washington, D.C.: Commission on Preservation and Access.
Wheeler, Jim. 1988. “Increasing the Life of Your Audio Tape."Journal of the Audio Engineering Society 36(April): 232-36.
Casey, Mike and Gordon, Bruce. 2007. Sound Directions: Best Practices for Audio Preservation. http://www.dlib.indiana.edu/projects/sounddirections/
Bigourdan , Jean-Louis, Reilly, James M., Santoro, Karen, Salesin, Gene. 2006. The Preserrvation of Magnetic Tape Collections: A Perspective. https://www.imagepermanenceinstitute.org/webfm_send/303