What is a Signal

Anything which carries information is a signal. A signal is a real (or complex) valued function of one or more real variable(s).When the function depends on a single variable, the signal is said to be one dimensional. A speech signal, daily maximum temperature, annual rainfall at a place, is all examples of a one dimensional signal. When the function depends on two or more variables, the signal is said to be multidimensional. An image is representing the two dimensional signal, vertical and horizontal coordinates representing the two dimensions A signal is a description of how one parameter is related to another parameter.

Types of Signal

For example, the most common type of signal in analog electronics is avoltage that varies with time. Since both parameters can assume a continuous range of values, we will call this a continuous signal. If this signal is passed through an analog-to-digital converter force each of the two parameters to be quantized. Signals formed from parameters that are quantized in this manner are said to be discrete signals. Discrete signals are quantized in one dimension ( as  discrete signal is obtained by sampling of a continuous signal the signal obtained will be discrete with respect to time axis and amplitude of the signal is continuous .  Digital signals are those which obtained by taking finite number of distinct values. Digital signals are discrete with respect to both time and amplitude. Digital signals are quantized in both dimension ( X-axis and Y-axis particular value exist; signal represented as just like a set of points in the plot depends on the sampling rate)