Background: The Library of Congress has large CD-Audio
collections dating from the earliest days of CD manufacture. CD-
ROMs are convenient media for access and temporary storage.
Unfortunately, such media are machine-dependent, so access is
contingent on surviving and working hardware and software.
Additionally, such media is subject to deterioration, just like
any other material. CD-ROMs are made of many layers, and the
materials used in these layers change over time, depending on
when the CD-ROMs were made and how they age. Depending on
susceptibility, wear, and environment, various layers of a CD
may undergo oxidation, hydrolysis or mechanical stress, leading
to damage (variously described as “rot” or “pin holes” or
“mirroring”, etc.). These and other phenomenon may lead to
errors in signal playback, which can be assessed by measuring a
disc’s “block error rate” or BLER. The greater the BLER, the
greater the loss of information. The Library of Congress has
long been committed to gaining an understanding of