11. Data reduction

As a rule, it is generally accepted that, when selecting a digital target format for original analogue or linear digital recordings, formats employing data reduction (frequently mistakenly called data "compression") based on perceptual coding (“lossy codecs”) must not be used. Transfers employing such data reduction result in the irretrievable loss of parts of the primary information. The results of such “lossy” data reduction may sound identical or very similar to the unreduced (linear) signal, but the further use of the data reduced signal will be severely restricted. These archival principles should also be applied, whenever possible, to the creation of original recordings made with the intention of being archived. If, however, contents come to an archive having been recorded on data reduced, non-linear format, such contents must be preserved faithfully. There is no objection, however, to the use of lossless, ie fully reversible compression.

Comment:
Data reduction is a powerful tool in the dissemination of audio signals. Its use is, however, counter to the ethical principle of preserving as much of the primary information as possible. Data reduction does not permit the restoration of the signal to its original acoustic condition and will, in addition, limit the further use of the recording because of the artefacts generated when cascading perceptually coded material - for example, in the making of a new programme incorporating the original sounds.

In the case of recordings originated in data reduced formats, a major problem with obsolescence of equipment may arise when the format of origination is of a proprietary character such as the MiniDisc and similar future systems (cf IASA-TC 04, 5.5.12.1).