Analogue versus Digital
Most of the quantities in nature that can be measured are continuous. Examples include Intensity of light during the day: Rise and fall in temper ature during a 24-hour period: Velocity of a car travelling from A to B: The measurable values generally change over a continuous range having a minimum and maximum value.
Digital representing of quantities Digital quantities unlike Analogue quantities are not continuous but represent quantities measured at discrete intervals. Consider the continuous signal as shown in the figure 1.1. To represent this signal digitally the signal is sampled at fixed and equal intervals. These number of samples do not exactly represent the original signal but only approximate the original continuous signal. If the number of samples that are collected is reduced by half, the reconstructed signal will be very different from the original due to under-sampling.