Analog and Digital Communication

The concept of information is central to communication. There is no precise definition of the word "information". So, instead of information, we deal with "message".

Message is defined as the physical manifestation of information as produced by the source

There are two distinct message categories:

Analog

An analog message is a physical quantity that varies with time usually in a smooth and continuous fashion.

Examples of analog messages are:

(i) the acoustic pressure produced when you speak

(ii) the angular position of an aircraft gyro

(iii) the light intensity at some point in a television image.

Digital

A digital message is an ordered sequence of symbols selected from a finite set of discrete elements.

Examples of digital messages are:

(i) letters printed on this page

(ii) listing of hourly temperature readings

(iii) the keys you press at a computer terminal.

Whether the message is analog or digital, it needs to be converted into an electrical signal. (There are only few messages, which are inherently electrical.)