CD players use a to scan the disc from the center outward along a spiral track. When the laser hits a pit , it scatters the light; when it hits a land , the light is reflected back to a sensor. The sensor translates these light changes into electrical signals (zeros and ones), which are then converted back into high-fidelity audio. The Compact Disc: An Introduction
A standard audio CD is a 120 mm (4.7 in) circular disc composed of several layers: audio compact disc
: A 1.2 mm thick layer of clear polycarbonate plastic . CD players use a to scan the disc