5.4.2 Selection of Best Copy Recordable media such as magnetic tape tend not to have multiple copies of the same generation. With the exception of cassette, audio on tape was only infrequently mass replicated and so the sound archivist must choose between generational duplicates. As a rule, the most original copy is the best copy to select for the purposes of preservation. However, the original tape may have suffered some form of physical or chemical degradation, such as hydrolysis, whereby a duplicate made in accordance with proper procedure prior to that decay might be better. Tape rarely shows visible signs of decay or damage so, where multiple copies of an item exist, the best approach is to carefully spool through, and then audition the tape to determine the best copy. Curatorial decisions must also be made to ensure that the most appropriate or complete duplicate is selected. This is primarily an issue where the tapes have been produced as a result of a sequential production process such as audio mastering or in the production of sound for film or video.