3. Choice of tapes and tape formats
If the highest standards are to be maintained, then the choice of tapes and tape formats is scarcely less important than the choice and maintenance of recording equipment. Because of its sturdy nature and its low sensitivity to humidity and temperature, and because it presents the least mechanical problems, the tape most widely used nowadays for archival purposes is polyester tape with a thickness of 52 micro-metres (1.5 mil). Several varieties of tape display good electro-magnetic qualities, are not significantly prone to print-through and are, therefore, suitable for archival purposes. For recording outside the studio long-play or double-play tapes are often the best sort to use because of the length of recording time they give, but care should be taken to make sure that these records are transferred to archival tape as soon as possible. It is impossible to say that anyone particular tape is 'the best', and the choice of tapes is usually a question of compromise between availability and price. As with the choice of equipment, one should bear in mind when choosing tapes, how many other similar institutions or radio stations use the same type. Furthermore, one should generally choose tapes which are likely to be available on sale for as long as possible, so that recording equipment does not have to be continually re-adjusted to compensate for different sorts of products. For the same reason it is advisable to purchase a large stock -about a year's supply -in advance and to ask for a batch from the middle of a production run. Care should be taken with new varieties of tapes, as the improved electro-magnetic qualities of a tape can often be accompanied by a fall-off in mechanical quality (such as its resistance to oxide shedding), at least during the period when a new tape is being brought onto the market. It makes better sense, therefore, to choose a somewhat older but proven product rather than risk losing valuable source material by using poorly tested products.
As efficient sound recording is a basic requirement for sound archives, it follows that high standards should be observed when choosing tape formats. The recording speed for original recordings and archival copies should never be less than 19 cm/s. For mono recordings one should use full-track, while for stereo recordings, halftrack should be used. For evaluation work and for distribution the expense can, of course, be tailored according to the requirements and for certain types of work compact cassettes are quite adequate in the quality they provide.