Making a CD
Putting the code on disc
As with other forms of sound recording, a compact disc begins when a microphone converts the sound waves into electrical signals.
The voltage of those signals is measured and coded electronically into binary digits. The digits then undergo further coding to link the two stereo channels into one pulse train, and to overcome damage to the signals from scratches or fingerprints that might occur during handling.
As a blank glass disc coated with a light-sensitive resin is spun under a laser beam, the coded signals are fed to the laser as electrical pulses.
It emits them as light flashes that cause a pattern of pits and flats on the coating - revealed once the coating is chemically developed. This gives far more accurate recording than with even the best conventional method.
The master disc provides a mould for reproduction. Each disc is given a thin aluminium coating to make it highly reflective, then lacquered for protection.