Compact discs, often called CD's, are round, flat plastic discs on which information is stored as a pattern of tiny pits and flat spaces on an audio CD's, information about recorded sound is contained in the pits and spaces. When the sound is recorded, a microphone translates the sound waves into electric signals. These signals are then divided into segments by electric circuit. For each second of recorded sound, there are 44,100 segments. The strength of each segment, which varies according to the original sound, is translated into a digital or numeric code. In this code, each sound segment is expressed as a series of electric pulses representing ones and zeros. During disk manufacturing, a laser uses the digital code as a pattern to guide the cutting of a spiral track of microscopic pits into the surface of one side of a blank disc. During the mass production of CDs, this pattern of pits is pressed on plastic discs. The discs are then covered with a thin reflective metal and given a clear plastic coating for protection. During playback in a CD player, a laser reads the pits. As the CD spins inside the player, a laser beam shines on the underside of the disk, which contains the pit spiral. The light is reflected by the disc's metal coating. The intensity of the reflection changes as the beam enters and leaves the pits. The reflected light strikes a device that translates these differences into an electric signal. This signal is a copy of the electric signal that was produced during the recording of the original sound. The CD player uses the electric signal to reproduce the original sound through loudspeakers or headphones.