ABSTRACT
Sound recordings belong to the group of audiovisual records. Textual documents have a high degree of redundancy and fault tolerance. The specific physical and chemical nature of audiovisual carriers in general, and of sound carriers in particular, is a factor in their increased vulnerability, as compared to paper-based documents. Coarse groove or 'shellac' discs were produced from around 1900 to the mid-1950s. Microgroove discs succeeded the shellac discs as mass replicated formats and were produced from the late 1940s to around 1990. Magnetic tape consists of two main parts: the support or base film and the magnetic layer. The greatest problem affecting magnetic tape stability is that of modern pigment binding materials introduced since the mid-1970s when polyester-polyurethane (PE-PU) binders were introduced. Magnetic tape is generally much less vulnerable to damage in replay than mechanical carriers.
