The Basics Of Cd Technology

The Basics of CD Technology Have you ever wondered why the CDs you burn don't look like commercially produced CDs? Here you go. . . .

What do you want to learn more about? CD-ROM discs A standard (pressed) CD-ROM disc consists of a layer of aluminum sandwiched between layers of lacquer and clear polycarbonate plastic. During molding, the polycarbonate base has minute indentations stamped into it. The highly reflective layer of aluminum is then applied to the polycarbonate base and sealed with a layer of lacquer to protect the disc surface from scratches and dust. The information on compact discs is represented by minute indentations in the polycarbonate base separated by the surface of the aluminum layer. The indentations are called pits, and the surfaces of the disc between pits are called lands. When the laser in a CD player or drive moves between pits and lands, the reflection is momentarily changed and processed as a one. Various lengths of pits and lands represent varying quantities of zeroes, which represent the original audio signal. Generally, the frequency of the audio signal is represented by the rate of change in the numbers, and the amplitude is represented by the magnitude of the numbers. Digital-to-analog converters process this binary data into music.

CD-R discs While commercially produced compact discs have pits molded into them during manufacturing, CD-Recordable (CD-R) discs are blank. CD-R discs contain a polycarbonate base, like the CD-ROM, but instead of the reflective aluminum layer, CD-R discs are covered with a layer of organic dye. There are four types of organic dye used in CDR discs: • • •

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Cyanine is considered the standard in recording and can be distinguished by its blue-green color. Metal-stabilized cyanine is visually indistinguishable from cyanine, but it is more resistant to age degradation. Phthalocyanine, which is pale blue, is considered by some to be superior in longevity but is virtually identical in quality to cyanine-based CDs. To protect the dye and serve as the reflective conduit, a thin layer of gold is applied to the dye. Azo is as durable as phthalocyanine dye. The use of a silver reflective conduit produces a bright blue color.

Instead of physically carving the pits, as standard CD-ROM pressing does, the CD recorder's laser burns the organic dye and creates marks in the disc's surface. To a CD player or CD-ROM drive, these marks appear the same as the stamped pits on a standard CD-ROM. As a result, CD-R discs can be read by most CD players or CD-ROM drives.