In electronics, a digital filter is an electronic filter (usually linear), in discrete time, that is normally implemented through digital electronic computation.
The parameters of digital filters are generally more stable than the parameters of analog (continuous) filters, primarily because the components of electronic filter change behaviour with temperature. Digital filters can be applied as optimal estimators. Digital filters are either finite impulse response (FIR) or infinite impulse response (IIR), though there is a third hybrid class of filters known as truncated infinite impulse response (TIIR) filters, which show finite impulse responses despite being made from IIR component.
Once a signal is in the digital form compatible with computers, it may be altered using digital filters. These are reasonably simple algorithms that can be implemented in software or hardware and can change a signal for a variety of purposes, including shaping it into a form suitable for transmission or storage, removing noise and distortion, sharpening edges in images, or minimizing interference with other signals. Such filters appear in virtually all components of communications systems and may be linear or nonlinear.
In signal processing, the function of a filter is to remove unwanted parts of the signal, such as random noise, or to extract useful parts of the signal, such as the components lying within a certain frequency range.