The tape produced is called the master tape. To make a compact disc, this tape is played and the sound signals sent to a CD cutter, which converts them into pulses of laser light. These etch pits in a blank disc, which is then copied to make CDs for the shops. When played, laser light reflected from the disc is changed into electrical signals. Amplifiers strengthen these signals.
Loudspeakers then turn the signals into sounds.
The pits on the underside of a CD are arranged in a spiral track, which starts at the centre of the disc and runs towards the outside edge. The track is only 1.6 millionths of a metre wide. It is etched on a disc of aluminium which is given a coating of plastic to protect it from damage.