Information is defined as the message, knowledge or a signal, which is passed from one place or person to another. The giver of the information is known as the informant. The point where the information originates is called the source and the point where it ends is called the destination.
There are many kinds of information source including men and machines, hence message appear in variety of forms.
These may be words, a sequence of discrete symbols or letters; it may be a single time varying quantity like the acoustic pressure produced by speech or music or the angular position of an aircraft gyro.
Based on the nature of their outputs, all the above information sources can be classified into two main categories. These are the analogue information sources and digital information sources.
Analogue information source emit one or more continuous amplitude while the output of digital information source consist of a sequence of discrete symbols or letters.