Compact Discs
One of the most important developments in sound reproduction in recent years has been the Compact Disc (CD). The original audio signal is converted into digital signals (see page 136) at a sampling rate of 44.1 kHz and using a 16-bit system. A version of these digital pulses is impressed on to a master disc using a laser. The latter produces a spiral track of indentations (‘pits’) in the surface. The regions between the pits are called ‘lands’. Moulds of the master are used to make the replay copies in a way that is not unlike the process used with vinyl discs.
Unlike a conventional vinyl record the spiral track on a CD starts at the centre and works outwards. The density of ‘information’ is very great: up to about 75 minutes ...
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