In signal processing, a filter is a device or process that removes some unwanted components or features from a signal. Filtering is a class of signal processing, the defining feature of filters being the complete or partial suppression of some aspect of the signal. Most often, this means removing some frequencies or frequency bands.

Filter (signal processing) Electronic filter, an electronic circuit which processes signals, for example to remove unwanted frequency components Digital filter, a system that performs mathematical operations to reduce or enhance certain aspects of a signal Analogue filter, a basic building block of signal processing much used in electronics

In signal processing, a digital filter is a system that performs mathematical operations on a sampled, discrete-time signal to reduce or enhance certain aspects of that signal. This is in contrast to the other major type of electronic filter, the analog filter, which is typically an electronic circuit operating on continuous-time analog signals.