Digital Signals

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An analog wave (A), and a digital rendition of this wave (B).
A SIGNAL IS DIGITAL WHEN IT CAN ATTAIN ONLY SPECIFIC LEVELS. THIS IS IN CONTRAST TO ANALOG signals or quantities that vary over a continuous range. A simple analog waveform is shown at top figure A; note that the amplitude varies smoothly over time. top figure B is an example of a digital approximation of the same signal.