1: Background
1.1 Audiovisual archives hold a responsibility for the preservation of cultural heritage covering all spheres of musical, artistic, sacred, scientific, linguistic and communications activity, reflecting public and private life, and the natural environment, held as published and un-published recorded sound and image.
1.2 The aim of preservation is to provide our successors and their clients with as much of the information contained in our holdings as it is possible to achieve in our professional working environment. It is the responsibility of an archive to assess the needs of its users, both current and future, and to balance those needs against the conditions and resources of the archive. The ultimate purpose of preservation is to ensure that access to the audio content of collection is available to approved users, current and future, without undue threat or damage to the audio item.
1.3 As the lifespan of all audio carriers is limited by their physical and chemical stability, as well as the availability of the reproduction technology and, as the reproduction technology itself may be a potential source of damage for many audio carriers, audio preservation has always required the production of copies that can stand for the original as preservation duplicates, which in the parlance of digital archiving have come to be known as “preservation surrogates”. The need to migrate content to another storage system applies to carriers of digital audio originals perhaps even more so as they may be endangered by the ever shorter lifetimes of highly sophisticated hardware and related software in the market, which, sometimes only a few years after their market introduction, will lead to the total obsolescence of replay equipment. However, the same constraints that apply to the original item will wholly, or in part, apply to the preservation target format, requiring continued reduplication. If preservation had continued by serial duplication in the analogue domain this would have produced a degradation of the audio signal with each subsequent generation.
1.4 The potential offered by the production of digital surrogates for the purpose of preservation seems to provide an answer to linked issues of preservation and access. However, the decisions made about digital formats, resolutions, carriers and technology systems will impose limits on the effectiveness of digital preservation that cannot be reversed, as will the quality of audio being encoded. Optimal signal extraction from original carriers is the indispensable starting point of each digitisation process. As recording media very often requires very specific replay technology, timely organisation of copying into the digital domain must take place, before obsolescence of hardware becomes critical.
1.5 The ability to recopy the captured digital copy without further loss or degradation has often led enthusiastic archivists to describe it as “eternal preservation”. The easy production of low bit-rate distribution copies broadens the ability of archives to provide access to their collections without endangering the original item. However, far from being eternal, poorly managed digital archiving practices may lead to a reduction in the effective lifespan and integrity of audio content, whereas a well managed digital conversion and preservation strategy will facilitate the realisation of the benefits promised by digital technology. Similarly, a poorly planned system requiring manual intervention may present a management task of considerable dimension that could be beyond the capabilities of the collection managers and curators and so endanger the collection. A well planned system should enable automation of the processes and so preservation can proceed in a timely manner. No system for preserving sound will provide a one-off solution; any preservation solution will require future transfers and migrations that must be planned for when the material is first digitised and stored.
1.6 The Guidelines address audio carriers such as cylinders and coarse groove discs, steel wire and office dictation systems, vinyl LP records, analogue magnetic tape, cassette and reel, magnetic digital carriers such as DAT and its video tape based predecessors, and optical disk media such as CD and DVD. Though many of the principles contained herein will be applicable, sound for film is not specifically addressed. This document does not consider piano rolls, MIDI files or other systems which are player directions rather than encoded audio. The following principles outline the areas in which critical decisions must be made in the transfer to and management of digital audio materials.
