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Introduction to Signals

Stefan Du Rietz  (e-mail: sdr at durietz.se)

What is a signal?

"A signal is a function (often of time) which conveys information about a physical system, usually about its state or behaviour." [1]

As the world is composed of physical systems, everything that can be quantitatively told about it is actually a signal.

By making measurements of different states of a system under controlled conditions, one can acquire a set of signals containing information about the dynamics of the system.

Applications of signals

Subsequent analysis and processing of these signals can reveal new information, not immediately apparent in the original signals, and transform the information into forms more suited to intuitive interpretation.

By means of the acquired signals, together with knowledge about the physical nature of the system, it may be possible to build a mathematical model of the system. The model can then be "run" in a computer to simulate different behaviours of the system. In this manner it is possible to test the system with various stimuli without disturbing the real system.


  1. Oppenheim AV, Schafer RW: Discrete-time signal processing, Prentice-Hall, Englewood Cliffs, NJ, 1989.

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