Introduction to Signals and Systems

Welcome to Introduction to Signals and Systems. This text will focus on the
properties of signals and systems, and the relationship between the inputs
and outputs of physical systems. We will develop tools and techniques to
help us analyze, design, and simulate signals and systems.

A signal is a pattern of variation of a physical quantity: a deļ¬nition which
covers a wide territory. You are processing signals as you read this text.
A lecturer creates a signal as he or she talks and your ear processes these
signals. Signals are all around us. Examples include acoustical, electrical,
and mechanical signals. Signals may depend on one or more independent
variables. As the name implies, one-dimensional signals depend on one
independent variable. An example is the location of a particle moving in a
rectilinear motion, in which case the independent variable is time, t .Two-
dimensional signals depend on two independent variables. An example is a
picture that varies spatially, in which case the independent variables are the
spatial coordinates, x and y.Many of the signals and systems that you have
routinely dealt with have interesting properties that this text will explore.
A system processes signals. For example, a compact disc (CD) player
is a system that reads a digital signal from a CD and transforms it into an
electrical signal. The electrical signal goes to the speaker, which is another
system that transforms electrical signals into acoustical signals. Many sig-
nals contain information. Other signals are used only to transport energy.
For example, the signal from a wall socket is boring in terms of information
content, but very useful for carrying energy