Signal processing is an important concept that is being used now days and it also forms an important subject in the various streams of Engineering. Here the sampling is the reduction of a continuous signal to a discrete signal. A sample here refers to a value or set of values at a point in time or space.
In signal processing the most important theorem used is Sampling Theorem which states as how to sample the given signal so that no information is lost in process. According to sampling theorem, a band limited signal with no frequency components above a certain cut-off frequency is uniquely determined by its discrete values at equally spaced points, provided these samples are taken at a sampling rate equal to or greater than twice the cut-off frequency or Fs >=2Fm. This minimum sampling rate is known as the Nyquist rate. The process of obtaining a set of samples from a continuous function of time x(t) is referred to as sampling. The process of sampling is done by the help of analog to digital converter filters.
A2D converters are the bread and butter of DSP systems. In real A/D converters the sampling is caried out by a sample-and-hold buffer. The sample-and-hold buffer splits the sample period in a sample time and a hold time. The signal is recovered at the reception side by the use of anti-aliasing filters or digital to analog converter.