5.5.10 Removal of Storage Related Signal Artefacts
5.5.10.1 It is preferable in most cases to minimise the storage related signal artefacts before undertaking digital transfer. Digital tapes should be re-spooled periodically if possible, and in any case always re-spooled before replay. Re-spooling reduces mechanical tension, which can damage the tape base or decrease performance during replay. Open reel digital tapes that have been left unevenly wound for some time may exhibit deformations, particular of tape edges, which may cause reproduction errors. Such tape should be rewound slowly to reduce the aberrations in the wind and rested for some months, which may aid in reducing replay errors. Though cassette systems can be similarly affected, the ability to influence the pack through reduced wind speed is not as great with such equipment.
5.5.10.2 Magnetic fields do not decay measurably in a period of time that is likely to affect their playability. The proximity of adjacent tracks or layers will not cause self erasure on analogue tapes, and in the unlikely event that it may cause issues with older digital tapes this is rarely critical as any resulting errors are within the limits of the system. Some loss of signal may be measurable in the oldest video based tapes when used to record digital audio. In these circumstances the lower coercivity of the magnetic particles and the apparent short wavelength on the tape caused by recording digital information using a rotating head combine to create the conditions where this may occur, at least in theory. This may make it difficult for replay equipment to track the information on the tape. All but the very earliest video tape formulations have a much higher coercivity, combined with systems which have better error correction technology, which made this problem largely irrelevant. In any event, attention to the cleanliness of the heads of the replay machine and tape will maximise the possibility of replay, as will careful alignment of the tape path.
5.5.10.3 Seriously damaged tapes may be recoverable using techniques that could be characterised as “forensic” due to their dependence on high-level skills from a range of scientific and engineering disciplines (see Ross and Gow 1999). Management of digital tape collections should aim to ensure copying occurs before un-correctable errors become a problem, as options for restoration of failed digital tapes are very limited.
