It is mandatory that transfers made from old to new archive formats be carried out with the intention of producing the closest possible surrogate. Above all, subjective alterations or “improvements”, such as de-noising or de-graining of film, must be avoided. Subjective alterations effectively rewrite the historical document according to the perspective of the operator undertaking the change, thus undermining the most basic principles of preservation.
The signal that the original recording engineer intended to capture is only part of a given audiovisual document. Unintended and undesirable artefacts (e.g., noise, distortions, drop-outs) are also part of it, whether caused by the limitations of historical recording technology, or subsequently added to the original signal by general use, mishandling or poor storage.
In some instances, apparent “imperfections” in a recording may be objectively corrected at the time of digitisation, by adjusting replay parameters to optimally retrieve the intended signal (see section 7). Generally speaking however, both the signal and the artefacts should be preserved with the utmost accuracy. It is essential that the full dynamic range, frequency response and/or image resolution of the original are transferred.
The careful documentation of all parameters chosen and procedures employed in the transfer process likewise is essential.
Comment:
Alterations in transferring from old to new formats are unavoidable in some circumstances, for example when converting an analogue composite video signal to a digital colour-difference bitstream.