Signal
When we plot a dependent variable with respect to an independent variable, it is called signal.
If we have one dependent variable and one independent variable, then it is called one dimensional signal. Example : Sinusoidal signal.
If we have more than one dependent variables and more than one independent variables, then it is called multidimensional signal. Example : Video signal.
1. Analog Signal
If we have a continuous variation of dependent variable with respect to a continuous variation of independent variable, then it is called analog signal or continuous time signal.
Which means that Analog signals are defined for every value of time and they take on continuous values in a given time interval.
Example : S (t) = 50 sin 100πt
2. Discrete Signal
If we have a continuous variation of dependent variable with respect to a descrete value of independent variable, then it is called discrete signal.
Since, descrete signals are defined for discrete value of time, they are also referred as descrete time signals.
However, it does not mean that dependent variable will not have values other than the values defined by the descrete value of independent variable. It may or may not have values at those instants but we can define them for some descrete values.
Example : S (nt) = 50 sin 100 πnt
where n = 0,1,2,3,4,…..
3. Digital Signal
If we have descrete dependent variable with respect to a desctere independent variable, then it is called digital signal.
Now, if we take a finite set of possible values of dependent variable and pick up only some of them which means these pick up values will be defined for some possible values of continuous variable, then the signal is called descrete time- descrete valued signal. This is also known as digital signal.