analog v. digital

Analog systems represent information about infinitely variable, real-world phenomena through corresponding signals that are also smooth and continuous. For example, changes in position, pressure, speed, sound, time, or temperature can be represented by analogous changes in voltage, or by the position of a needle on a dial. Digital information is measured in discrete, quantized values. When an analog signal, such as sound, is digitized, samples are taken at regular intervals, rounded to approximate values, and stored as numbers.

• Analog signals have infinite resolution. Digital signals are inherently granular. The fidelity of a digital signal is limited by its sampling rate and bit depth.
• Analog information is susceptible to noise - undesirable random variations that reduce the signal’s clarity. These errors can accumulate when analog information is transmitted over long distances, or through generation loss if a recording is copied and recopied. Analog media, like tapes and vinyl records, can degrade with repeated use. Digital communication and copying can be completely error-free, particularly when error detection and correction techniques are used.
• In digital communications, the sender and receiver must both know, in advance, the rules governing how symbols are encoded, transmitted and converted back into an analog waveform. Foreknowledge of the ‘language’ being used is generally not necessary in analog communications, which can be sent, reproduced, and processed without complicated conversions.

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wiseGEEK on analog v. digital

Wikipedia on analog recording v. digital recording