7. Optimal signal retrieval from original carriers

Optimal retrieval of the signal on analogue recordings can only be achieved by modern, well maintained replay equipment, ideally of the latest generation, in order to keep replay distortions to the absolute minimum. When replaying historical formats, replay parameters (speed, playback equalisation, track format etc) must be chosen objectively and be based upon knowledge of the given historical format. The replay equipment has to be optimally adjusted to the correct parameters and any experimentation with settings must be done using a straight copy of the original recording. In order to keep possible damage to the original carriers to minimum, replay equipment must be regularly maintained to professional standards. To aid in this and to diagnose emerging problems, calibration media suitable for the replay equipment must be used whenever obtainable.

For digital originals, the same principles apply. It must be noted, however, that despite nominal format compatibility, minor - or even major - differences may occur between different players when retrieving signals from the same carriers. In order to detect such problems, error monitoring during replay is imperative.

In addition, it must be noted that format incompatibilities may be discovered in some digital formats when trying to retrieve the various kinds of sub-code information.

It is not an easy task to assess the correct replay parameters for a given analogue sound document if objective information on the recording format parameters is missing. As in other fields of historical research, the use of cautiously chosen approximations is permissible when necessary. As a matter of principle, however, irreversible steps must be avoided. Subjective treatments must only be applied to access copies.

The systematic retrieval of sub-code information of digital originals, especially that contained in original R-DAT recordings, is still a widely neglected chapter in the safeguarding of useful secondary information. The reasons are due mainly to incompatibilities of sub-codes as not all players and interfaces support all sub-codes. As yet, no routines have been developed for the further safeguarding of this information in other than the original format. Compatibility problems often also occur in the replay of recordable or rewritable optical disks.

It should also be noted that several recent digitisation projects have suffered from inadequate signal retrieval from original documents because of the lack of professional knowledge and the appropriate equipment.