The effects of repeated copying and recording media on intelligibility

The increasing use of MiniDisc technology for audio harvesting by law enforcement agencies gives some cause for concern. The reasons for its use are understandable: the kit is small, cheap, light and easy to use. However, there are disadvantages when compared to some of the existing technologies, due to the use of bit reduction techniques. In order to demonstrate the potential problems associated with MiniDisc technology, a two-factor design experiment was set up in which listeners were asked to listen to representative lists of words, contaminated with speech babble. The two factors of interest were (1) type of medium (e.g. analogue tape, MiniDisc) and (2) the generation copy. It was found that the copying process of MiniDiscs affects the quality of the signal in an unpredictable manner: it could improve but also deteriorate the signal. Quality could be deteriorated but intelligibility could have improved. The effects of different types of MiniDisc equipment vary due to different compression techniques. In addition, the superior quality of DAT and the inferior quality of analogue tapes was confirmed.