Analysis of aged CD-R: From optical HF signal defects to digital errors

This article focuses on the CD-R defects that cause digital errors when decoding the HF signal delivered by the optical pickup of a player. We often remark that the error rate is not correlated with any of the parameters currently used to qualify the HF signal. We develop a more precise analysis of the HF signal than those of the analysers, in order to explain how errors happen in this case. The information is obtained mainly from the complete histogram of the positions of the transitions. We also check particular signal segments such as the beginnings of data frames. Using these analysis tools, we highlight different kinds of defects on aged CD-R. One of them consists in micrometre-sized dark spots, which are localized on the dye layer. More generally, the defects due to ageing cannot be characterised only by the standard parameters given by analysers.

► The study concerns the decrease in quality of CD-R due to ageing.
► We develop a more accurate analysis than those of the available analysers.
► Different kinds of defects are highlighted.
► Micrometre-sized dark spots are detected on some CD-R.
► Exposure to light causes a homogeneous loss of contrast of the HF signal.