Digital Signal Processing Reference
In-Depth Information
Chapter 2
Signals in the time and frequency domain
From a physical point of view signals are oscillations or waves. They are imprinted with
certain information by changing according to a certain pattern.
Only electrical or electromagnetic signals are used in information technology. They have
incomparable advantages compared with other forms of signals - e.g. acoustic signals.
Electric signals ....
•
spread at (almost) the speed of light,
•
can be directed by means of cables to where they are needed,
•
can be transmitted around the world and even into space by means of
aerials through the atmosphere and vacuum without cables,
•
are unrivalled in the way they can be received, processed and
transmitted accurately and interference-proof,
•
use hardly any energy compared with other electrical and mechanical
systems,
•
are processed by the tiniest of chips which can all be manufactured very
cheaply (fully automated production in large series),
•
when used properly they do not pollute the environment and are not a
health hazard.
If a signal contains information then there must be an infinite number of different signals
as there is an infinite variety of information.
If one wanted to know everything about all signals and how they react to processes or
systems, a course of study would inevitably tend to be infinitely long too. Since this is not
possible it is necessary to look for a way of describing all signals according to a unified
pattern.
The FOURIER Principle
The FOURIER Principle makes it possible to regard all signals as composed of the same
unified "components". Simple experiments with DASY
Lab
or with a signal generator
("function generator"), an oscilloscope, a loudspeaker with a built-in amplifier and - most
important ! - your sense of hearing, lead to the insight which the French mathematician,
natural scientist and advisor to Napoleon discovered mathematically almost two hundred
years ago.
