In geoscientific signal processing, a digital filter is a system (usually a time-invariant,
linear
operator realized by a computer program) that performs mathematical operations on
a sampled,
discrete-time signal to reduce certain aspects and/or enhance certain other aspects
of that signal.
The term “digital” is meant in contrast with the other major type of filters, the
analog filter,
which is used during signal-recording and is typically realized by an electronic circuit
operating
on continuous-time analog signals.