In response to the proposal of digitizing the entire back-run of several European audio archives, many research projects have been carried out in order to discover the technical issues involved in making prestigious audio documents digitally available, which are related to the A/D transfer process and supervised metadata extraction. This article gives an innovative approach to metadata extraction from such a complex source material. This article also describes the protocols defined, the processes undertaken, the results ascertained from several audio documents preservation projects and the techniques used. In addition, a number of recommendations are given for the re-recording process, aimed at minimizing the information loss and to automatically measure the unintentional alterations introduced by the A/D equipment.