An analog filter uses analog electronic circuits made up from components such as resistors, capacitors and op
amps to produce the required filtering effect. Such filter circuits are widely used in such applications as noise
reduction, video signal enhancement, graphic equalisers in hi-fi systems, and many other areas.
There are well-established standard techniques for designing an analog filter circuit for a given requirement.
At all stages, the signal being filtered is an electrical voltage or current which is the direct analogue of the
physical quantity (e.g. a sound or video signal or transducer output) involved.
A digital filter uses a digital processor to perform numerical calculations on sampled values of the signal. The
processor may be a general-purpose computer such as a PC, or a specialised DSP (Digital Signal Processor)