How is sound digitized?

Sound is a time dependent pressure variation in air. A microphone translates this to a varying voltage on a wire. Analog recorders record this signal by storing the varying voltage on magnetic tape as a varying magnetization in a strip of tape coated with a magnetic material. Digital recorders first digitize the signal by rapidly taking samples of the voltage, perhaps 30000 samples every second. Each sample is then digitized by a device called an A-D converter. The digital numbers from this converter are stored digitally in various ways, eg, in pits cut in a disc by a laser. The A-D converter is the heart of the digitization process. Typically it is a chip sold by one of several companies. How this works is too complicated for the space we have here. Look at this reference for more info. http://en.wikipedia.org/wiki/Analog-to-digital_converter