SIDEBAR: How digital filters work by Technical Analysis, Inc.
Filters are tools for "tuning into" parts of the total energy contained in an information stream. For
example, all of the information transmitted on the AM radio stations near you arrives at your car radio. If
you tried to listen to it all, you would hear a terrible, useless din. But with your radio's dial, you can
adjust the "center frequency" of the radio's filter, and select the one station you want to hear. In essence,
the filter operates as an electronic door, which can be slid along the dial, letting some of the energy
through. If the door is shaped properly, only one station at a time can get through.