Signals and Systems - Electrical Engineering

CHAPTER 1 Continuous-Time Signals.........................................................................

A journey of a thousand miles

begins with a single step.

Lao Tzu (604–531BCE)

Chinese philosopher

1.1 Introduction

In this second part of the book, we will concentrate on the representation and processing of
continuous-time signals. Such signals are familiar to us. Voice, music, as well as images and video
coming from radios, cell phones, IPods, and MP3 players exemplify these signals. Clearly each of
these signals has some type of information, but what is not clear is how we could capture, represent,
and perhaps modify these signals and their information content.

To process signals we need to understand their nature—to classify them—so as to clarify the limita-
tions of our analysis and our expectations. Several realizations could then come to mind. One could
be that almost all signals vary randomly and continuously with time. Consider a voice signal. If you
are able to capture such a signal, by connecting a microphone to your computer and using the hard-
ware and software necessary to display it, you realize that when you speak into the microphone a
rather complicated signal that changes in unpredictable ways is displayed. You would ask yourself
how is it that your spoken words are converted into this signal, and how could it be represented
mathematically to allow you to develop algorithms to change it. In this book we consider the rep-
resentation of deterministic—rather than random—signals, clearly a first step in the long process of
answering these significant questions.

A second realization could be that to input signals into a computer the signals must be in binary
form. How do we convert the voltage signal generated by the microphone into a binary form? This
requires that we compress the information in a way that permits us to get it back, as when we wish
to listen to the voice signal stored in the computer.

Signals and Systems Using MATLAB®. DOI: 10.1016/B978-0-12-374716-7.00004-1
©c2011, Elsevier Inc. All rights reserved. 65