a device that outputs a signal where each sample is given by a linear combination of past and present input samples and past output samples (assuming we want to restrict the discussion to causal systems)
Software configured filters that are used to condition digitized signals utilizing DSP's (Digital Signal Processor's) or hardware structures such as certain types of Gate Arrays. These structures can be configured to mathematically manipulate digital data to provide the equivalent of analog filters or to produce filters not realizable in the analog world.
An algorithm operating upon a sequence of discrete-time sampled data, designed to pass signals with selected temporal or spatial frequencies while attenuating signals with other temporal or spatial frequencies. Such filters are often used to pass desired signals while suppressing noise or interfering signals. Common types are low-pass filters, which suppress high-frequency energy; high-pass filters, which reject low-frequency energy; and bandpass filters, which reject low- and high-frequency energy, and pass only a limited range of frequencies in between.
A filter that's implemented digitally. A digital filter accepts digital inputs (typically samples read from an A/D converter) and produces digital outputs. The data is processed in firmware running on a DSP. [ more
In electronics, a digital filter is any electronic filter that works by performing digital mathematical operations on an intermediate form of a signal. This is in contrast to older analog filters which work entirely in the analog realm and must rely on physical networks of electronic components (such as resistors, capacitors, transistors, etc.) to achieve the desired filtering effect.