What happens inside a CD player?

An infrared laser is focused onto the metallic reflective layer of the disc, where a spiral track of “pits” and “lands” represents the zeros and ones of digital signals. The return signal is converted by a photodiode sensor into a digital electric signal, which is converted to analog form for reproduction of the original recorded sound. Optical recording, introduced by the Sony Corporation and Philips Electronics NV in 1982, allows accurate reproduction of sound over virtually the entire range of human hearing.