Format Deviations
Some major recording publishers have begun to sell CDs that violate the Red Book standard. Some do so for the purpose of copy prevention, using systems like Copy Control.
Some do so for extra features such as DualDisc, which includes both a CD layer and a DVD layer whereby the CD layer is much thinner, 0.9 mm, than required by the Red Book, which stipulates a nominal 1.2 mm, but at least 1.1 mm. Philips and many other companies have warned them that including the Compact Disc Digital Audio logo on such non-conforming discs may constitute trademark infringement. Either in anticipation or in response, recent copy-protected CDs bear stickers and warnings that the CD is not standard and may not play in all CD players, and no longer display the long-familiar logo.
DVD Audio, an advanced version of the audio CD, emerged in 1999. The format was designed to feature audio of higher fidelity. It applies a higher sampling rate and used 650 nm lasers.
Read more about this topic: Session (CD)