The function of a filter is to

Filters, as the name implies, are devices that filter waves. "Wave" is a very wide range of physical concepts, in the field of electronics, "wave" is narrowly confined to the process of describing the value of a variety of physical quantities with the ups and downs of time. This process is converted into a voltage or current as a function of time by the action of various types of sensors, called the time waveform of the various physical quantities, or a signal. Because the independent variable time 'is a continuous value, so it is called a continuous time signal, but also customarily referred to as an analog signal (Analog Signal). With the generation and rapid development of digital computer (generally referred to as computer) technology, in order to facilitate the computer processing of signals, produced under the guidance of the sampling theorem will be transformed into a continuous time signal discrete time signal of the complete theory and method. In other words, you can only use the original analog signal in a series of discrete time coordinates on the sample value to express the original signal without losing any information, waves, waveforms, signals, these concepts since the expression of the objective world is a variety of physical changes, naturally, is the modern society relies on a variety of information carriers. Information needs to be disseminated, relying on the transmission of waveform signals. Signal in its generation, conversion, transmission of each link may be due to the environment and the presence of interference and distortion, and even in many cases, this distortion is still very serious, so that the signal and the information it carries is y buried in the noise.

?