Filters are systems or elements used to remove substances such as dust, dirt, or electronic signals. They can be used to filter air or gases, fluids, as well as electrical and optical phenomena. A filter is a device or process that eliminates certain aspects of a signal. This suppression of certain frequencies is the defining characteristic of filters. A filter is a circuit that can pass (or amplify) certain frequencies while attenuating others.
This means that it can extract important frequencies from signals that also contain unwanted or irrelevant frequencies. In signal processing, a filter is a device or process that removes some unwanted components or characteristics from a signal. Filtering is a kind of signal processing, and the defining characteristic of filters is the complete or partial suppression of some aspect of the signal. In most cases, this means eliminating some frequencies or frequency bands. However, filters do not only operate in the frequency domain; especially in the field of image processing, there are many other objectives for filtering.
Correlations can be eliminated for certain frequency components and not for others without having to act in the frequency domain. Filters are widely used in electronics and telecommunications, radio, television, audio recording, radar, control systems, music synthesis, image processing and computer graphics. They are essential for many applications and can be used to improve the quality of signals.