Compact Disc Digital Audio

Compact Disc Digital Audio (CDDA or CD-DA), also known as Digital Audio Compact Disc or simply as Audio CD, is the standard format for audio compact discs. The standard is defined in the Red Book, one of a series of Rainbow Books (named for their binding colors) that contain the technical specifications for all CD formats. The first commercially available audio CD player, the Sony CDP-101, was released in October 1982 in Japan. The format gained worldwide acceptance in 1983–84, selling more than a million CD players in those two years, to play 22.5 million discs. Beginning in the 2000s, CDs were increasingly being replaced by other forms of digital storage and distribution, with the result that by 2010 the number of audio CDs being sold in the U.S. had dropped about 50% from their peak; however, they remained one of the primary distribution methods for the music industry. In the 2010s, revenues from digital music services, such as iTunes, Spotify, and YouTube, matched those from physical format sales for the first time. According to the RIAA's midyear report in 2020, phonograph record revenues surpassed those of CDs for the first time since the 1980s. The optophone, first presented in 1931, was an early device that used light for both recording and playback of sound signals on a transparent photograph. More than thirty years later, American inventor James T. Russell has been credited with inventing the first system to record digital media on a photosensitive plate. Russell's patent application was filed in 1966, and he was granted a patent in 1970. Following litigation, Sony and Philips licensed Russell's patents for recording in 1988. It is debatable whether Russell's concepts, patents, and prototypes instigated and in some measure influenced compact disc's design. The compact disc is an evolution of LaserDisc technology, where a focused laser beam is used that enables the high information density required for high-quality digital audio signals.