Tape Degradation Factors and Challenges in Predicting Tape Life (2008)

From its introduction in Germany in 1935 and its worldwide rise to the primary medium for audio recording in the late 1940s and 1950s, magnetic tape earned a deserved reputation as a reliable and high-quality storage medium. (1) There are vast archives of magnetic tape that contain information that needs to be preserved. As Dietrich Schuller (2) so aptly stated, world's stock of audio recordings is estimated to be more than 50 Mh (million hours) of materials.... None of these recordings are on permanent carriers ... The following claim was found in promotional material for a Workshop: Audiovisual Preservation for Culture, Heritage and Academic Collection on the Digitization 101 Blog. Seventy percent of all audiovisual material is under immediate threat of deterioration, damage or obsolescence--and seventy percent of collection managers don't know it. Surveys have found serious shortages of trained staff and equipment, and an even more serious shortage of concerted preservation actions. The immediate needs are: awareness and help. (3) The present author became more widely involved with audio preservation and restoration in 2001 while transferring 51 reels of the oldest tapes in the U.S. (4) This work became a full-time career in 2004, and the need for further research into the degradation modalities of magnetic tape became obvious. This paper provides a review of tape types and their degradations and addresses what is known, what is hypothesized, and where more research is required. Brief Chronology of Tape Types 1932 Magnetic tape development underway at Ludwigshafen, Germany (5) 1935 Magnetophonband Typ C coated acetate tape 1944 Magnetophonband Typ L homogeneous PVC tape 1950s Back coating introduced in Europe 1953 First PET tape from 3M 1960s Back coating becomes widespread 1972 BASF ceases production of PVC tape 1972/73 3M/Scotch ceases production of acetate tape Current status The use of analog tape declined rapidly at the end of the 20th century, with the major tape manufacturers consolidating and/or spinning off their tape operations and most of them ultimately closing or substantially restructuring. Manufacture of high-end analog audio tape recorders has virtually ceased. (6) Many musicians and recording engineers prefer the sound of analog for recording, so new material is still being generated, complicating archival strategies. Conceptual timeline Many factors influence the overall quality of a digital copy of an original analog tape, including (1) the condition of the original tape based on inherent and external degradation factors, (2) the original quality and state of maintenance of the tape reproducer (considering few if any additional quality reproducers will be manufactured), and (3) the quality of the digitization. The overall transfer quality is the product of all of these factors, as conceptually shown in Figure 1. [FIGURE 1 OMITTED] While the exact shapes of the curves vary with each tape format and type, the factors remain the same. The Reproducer Quality curve includes the availability of technicians skilled in the ability to maximize playback quality as well as to recognize and to treat problems as they are encountered. Since the publication of the original AES preprint of this paper in 2006-10, there has been discussion as to whether this graph is optimistic or pessimistic. There are, of course, many variables involved, but it should be possible to maintain certain models of at least reel-to-reel players--or perhaps even construct new ones--at least through 2035 and perhaps further into the future. This timeline and comments made under acetate tape are not meant to reduce the pressure to digitize now. Rather, it is meant to show that the time is short considering the amount of digitization that needs to be done. Current best practice is to digitize tapes sooner rather than later and to store these digital files in managed repositories and distribute copies to minimize the effects of catastrophic loss of a single archives. …