Researchers for Philips began using video Laserdisc technology in the early 1970s to experiment with audio-only optical discs. After initially using wideband frequency modulation (FM), the researchers then started utilizing digitized PCM audio signals. By the end of the 1970s, other companies created their own audio disc prototypes. One of those companies, Sony, began working with Philips in 1979. The collaboration resulted in the creation of a taskforce of engineers from both corporations whose assignment was designing a new digital audio disc or compact disc.
A year later the taskforce produced a compact disc standard, the “Red Book.” In late 1982 the compact disc, or CD, reached the market in Asia. It reached other markets early the following year. Two years after that, in 1985, a compact disc was made for another application. The CD-ROM (read-only memory) made it possible to contain massive amounts of computer data instead of digital sound. In the early 1990s a user-recordable CD for data storage, CD-R, was introduced. CD-R became the standard for exchanging and archiving of computer data and music.
The compact disc has evolved from its original purpose of storing digital audio. The CD has done much more than become the standard playback format for commercial audio recording. The optical discs are now being used to store many other types of digital data. Two and a half decades after a taskforce was created for its design, the compact disc has been very successful. CD-Audio, CD-ROM, and CD-R totaled approximately 30 billion discs sold in 2004.
CD-Audio still stores data in a format compliant with the Red Book standard. Up to 99 stereo tracks can be stored on an audio CD. Although there are 80-mm versions available in “business-card” and circular form, standard compact discs have a diameter or 120 mm. Most 120-mm audio CDs can hold 74 minutes of audio. There are some versions that are capable of holding 80, 90, and even 99 minutes of audio. The 80-mm discs can only hold 20 minutes of audio.
The length of audio CDs was a factor in it becoming popular. Its 74-minutes of playing time was longer than that of most long-playing vinyl albums. This was an advantage during the early years of CDs while the two formats were in competition for control of the marketplace. Audio CDs would often be released with one or more extra or bonus tracks, which would entice consumers to buy the compact disc version for the extra material that they could not get on the vinyl album.
A three letter code is printed on the back of many audio CDs. The “A” of the code stands for analog, while the “D” stands for digital. The code was used even more frequently on early CDs. The breakdown for the code is that the first letter represents how the album was recorded, the second represents how the album was mixed, and the third represents how it was transferred (this was always a “D” because a CD is a digital medium). Due to this early code structure, most early CDs are “AAD” (analog recording and mixing, digital transfer to CD). The code was frequently followed by a brief description such as “Full Digital Recording for DDD and “Digitally Mixed Analog Recording” for ADD. Bob Till You Drop by Ry Cooder was the first digitally recorded popular music album. The 1978 recording was unmixed and recorded directly to a two-track 3M digital recorder in the studio. Early adherents of digital recording included top recording artists such as Stevie Wonder. Wonder took advantage of the technology in 1979 for Journey Through the Secret Life of Plants and his subsequent recordings. Although he was among those who felt that the multitrack digital recording technology of the early 1980s was not as sophisticated as the analog systems, former Beatles producer George Martin utilized digital mixing to eliminate the noise and distortion that would be introduced by using an analog master tape. One example of a digitally mixed analog recording was Fleetwood Mac’s Tusk in 1979. Digital recoding and mixing was becoming commonplace among recording artists and producers who were known for having an interest in fidelity by the time compact discs were introduced worldwide.