Essentially, the process of analog to digital conversion allows for an analog signal to be converted into digital signal which can be stored in computer memory for required processing. Analog signals are 'real world' signals and need to be digitized in discrete forms in order for the computer to be able to manipulate the data. To process the everyday analog signals digitally requires the conversion of the natural signals to discrete forms (discrete time and discrete amplitude variations) which offer many advantages.
The process of representing analog or continuous time signals x(t) by discrete values x[n] at uniformly equally spaced or unequally spaced in time, is known as sampling. Sampling places a critical role in many application domains such as communication, video and controls. When signals is sampled, we record a value. Sampling can lead to many data values and processing of data values is more flexible to deal with. After sampling, we can accurately reconstruct any continuous-time signal from its samples as long as the sampling frequency FT is at least twice as large as the highest frequency component of the original signal.