THE TASK OF SAFEGUARDING
The basic procedure for restoring an audio carrier is practically identical for every type of carrier. In the first phase - listening - the more obvious necessary actions are identified; the process then moves on to high definition copying on a computer system and spectroscopic analysis. Some (semi-)automatic modules exist that are used for reducing or eliminating common problems: they are the so-called declicker and decrackler modules, etc. Other operations are performed manually, such as, for instance, the elimination of transients through cuts, or the non linear compression/expansion of the sound and its filtering through equalizers of various types. The manual operations are carried out at the discretion of the technician and the end user and may require working times lasting up to 60 times the duration of the track (to correct 1 minute of modulation can take up to 1 hour, for instance).
The Swiss National Sound Archives remains consistent with its mandate even it does jobs of a commercial nature. The fundamental principle on which it bases its work is: the extraction of the best possible sound from the original carrier through the use of the most suitable reproduction device, and subsequent processing aimed at reconstructing a sound that is the most faithful possible to the original performance or production. Any other type of intervention is possible, but does not come within the scope of the tasks of the Swiss National Sound Archives.
Example of an audio restoration
Le Quatuor de Flonzaley: String quartet, no. 1, op. 41, in a minor (Robert Schumann); Camden, 10.05.1918; VICTROLA; 6115; C 6115 A 3 2; E 6115 B 3 3 (HR4744_A extract)