对于“信号”这个词，我们已经很熟悉了。所有承载信息的东西都可以称为信号，例如交通信号、求救信号，甚至还有烟雾信号。在纸牌游戏中，当我们拿到一手好牌的时候，往往尽量不给对方透露任何“信号”。那么，处理信号意味着什么呢？本书将采用现实生活中大家所熟悉的信号和信号处理方法，以最为简洁明了的方式解答这个问题。
大家可能没有意识到，实际上信号和信号处理时时刻刻影响着我们的日常生活。本书不仅展示了为什么信号和信号处理广泛存在于我们的日常生活中，而且更深入地解释了其中的原理。例如，为什么我们从收音机中听到的声音效果要远好于从手机中听到的声音效果？本书面向的读者是非技术类的人群，而不是工程专业的学生。因此，本书的主要目的有两个：首先，采用最少的数学公式，以通俗的方式阐述信号和信号处理的基本概念与原理；其次，介绍信号处理中的“语言”—术语。（为了便于阅读，本书在最后附上了完整的信号处理术语和缩写词。）对于那些在公司制作或者使用信号处理硬件或软件的非技术类读者，本书将会是你的最佳选择。日常工作中，你可能会碰到许多看似神秘的概念和术语。本书将为你揭开这一层神秘的面纱，让你更深入地理解信号处理，从而更有效地与工程师或者其他技术类人员交流。
通常可以将信号分为两大类：模拟信号和数字信号。本书将逐步解释这两种信号的本质，以及如何在日常生活中使用它们来提高生活品质。
本书的章节是按照作者的理解安排的，你不必按照章节依次阅读，也不见得要阅读整本书。第1章主要介绍信号处理如何在近现代变得如此重要及其原因。第2～5章则阐述模拟信号和数字信号的基本性质。其他章节介绍模拟信号和数字信号的处理方法。
全书的内容大致如此。我们希望你能喜欢这本书，还望它能给你带来帮助。
Contents
1 What Is Digital Signal Processing? 1
The Phantom Technology 1
What Is a Signal? 2
Analog and Digital Signals 3
Digital Signal Processing 3
What You Should Remember 5
2 Analog Signals 7
What Is an Analog Signal? 7
A Temperature Analog Signal 7
An Audio Analog Signal 8
An Electrical Analog Signal 10
What Is an Electrical Voltage? 10
Sinusoidal Wave Voltages 13
Other Useful Periodic Analog Signals 19
A Human Speech Analog Signal 21
What You Should Remember 22
3 Frequency and the Spectra of Analog Signals 25
Frequency 25
Cycles per Second 26
Radians per Second 28
The Concept of Spectrum 29
Analog Signal Spectra 30
A Composite-Signal Spectral Example 32
Harmonics 34
Harmonic Distortion 37
Bandwidth 39
The Other Bandwidth 42
What You Should Remember 42
4 Digital Signals and How They Are Generated 43
What Is a Digital Signal? 43
The Notion of Digital 43
Digital Signals: Definition #1 44
Digital Signals: Definition #2 45
How Digital Signals Are Generated 48
Digital Signal Generation by Observation 48
Digital Signal Generation by Software 48
Digital Signal Generation by Sampling an Analog Signal 49
The Sample Rate of a Digital Signal 52
A Speech Digital Signal 53
An Example of Digital Signal Processing 55
Another Example of Digital Signal Processing 57
Two Important Aspects of Sampling Analog Signals 61
Sample Rate Restriction 62
Analog-to-Digital Converter Output Numbers 62
Sample Rate Conversion 63
Decimation 63
Interpolation 63
What You Should Remember 66
5 Sampling and the Spectra of Digital Signals 67
Analog Signal Spectra—A Quick Review 67
How Sampling Affects the Spectra of Digital Signals 71
The Mischief in Sampling Oscillating Quantities 73
Sampling Analog Sine Wave Voltages 76
Why We Care about Aliasing 80
The Spectrum of a Digital Sine Wave Signal 82
The Spectrum of a Digital Voice Signal 85
The Spectrum of a Digital Music Signal 86
Anti-Aliasing Filters 89
Analog-to-Digital Converter Output Numbers 93
What You Should Remember 94
6 How We Compute Digital Signal Spectra 95
Computing Digital Spectra 95
The Discrete Fourier Transform 96
The Fast Fourier Transform 96
A Spectral Computation Example 97
The Computations 97
What the Computations Mean 103
A Spectral Analysis Example 103
What You Should Remember 106
7 Wavelets 107
The Fast Fourier Transform (FFT)—A Quick Review 107
The Continuous Wavelet Transform (CWT) 109
Undecimated or Redundant Discrete Wavelet Transforms (UDWT/RDWT) 114
Conventional (Decimated) Discrete Wavelet Transforms (DWT) 114
What You Should Remember 117
8 Digital Filters 119
Analog Filtering 119
Generic Filter Types 121
Digital Filtering 122
What You Should Remember 126
9 Binary Numbers 127
Number Systems 128
Decimal Numbers, a Base-10 Number System 128
A Base-4 Number System 129
Binary Numbers, a Base-2 Number System 130
Using Binary Numbers at Home 132
Binary Data 133
Why Use Binary Numbers? 134
Digital Hardware Is Easy to Build 134
Binary Data Is Resistant to Degradation 135
Binary Numbers and Analog-to-Digital Converters 136
What You Should Remember 139
A Scientific Notation 141
B Decibels 145
Decibels Used to Describe Sound Power Values 146
Decibels Used to Measure Earthquakes 147
Decibels Used to Describe Signal Amplitudes 149
Decibels Used to Describe Filters 153
C AM and FM Radio Signals 155
AM Radio Signals 155
FM Radio Signals 157
Comparing AM and FM Radio 159
D Binary Number Formats 161
Unsigned Binary Number Format 161
Sign-Magnitude Binary Number Format 162
Two’s Complement Binary Number Format 163
Offset Binary Number Format 165
Alternate Binary Number Notation 166O
ctal Binary Number Notation 166
Hexadecimal Binary Number Notation 166
Glossary 169
目录
第1章 什么是数字信号处理 1
幻影技术 1
什么是信号 2
模拟信号和数字信号 3
数字信号处理 3
本章要点 5
第2章 模拟信号 7
什么是模拟信号 7
温度模拟信号 7
音频模拟信号 8
电子模拟信号 10
什么是电压 10
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