對于“信號”這個詞，我們已經很熟悉了。所有承載信息的東西都可以稱為信號，例如交通信號、求救信號，甚至還有煙霧信號。在紙牌游戲中，當我們拿到一手好牌的時候，往往盡量不給對方透露任何“信號”。那么，處理信號意味著什么呢？本書將采用現實生活中大家所熟悉的信號和信號處理方法，以最為簡潔明了的方式解答這個問題。
大家可能沒有意識到，實際上信號和信號處理時時刻刻影響著我們的日常生活。本書不僅展示了為什么信號和信號處理廣泛存在于我們的日常生活中，而且更深入地解釋了其中的原理。例如，為什么我們從收音機中聽到的聲音效果要遠好于從手機中聽到的聲音效果？本書面向的讀者是非技術類的人群，而不是工程專業的學生。因此，本書的主要目的有兩個：首先，采用最少的數學公式，以通俗的方式闡述信號和信號處理的基本概念與原理；其次，介紹信號處理中的“語言”—術語。（為了便于閱讀，本書在最后附上了完整的信號處理術語和縮寫詞。）對于那些在公司制作或者使用信號處理硬件或軟件的非技術類讀者，本書將會是你的最佳選擇。日常工作中，你可能會碰到許多看似神秘的概念和術語。本書將為你揭開這一層神秘的面紗，讓你更深入地理解信號處理，從而更有效地與工程師或者其他技術類人員交流。
通�？梢詫⑿盘柗譃閮纱箢悾耗M信號和數字信號。本書將逐步解釋這兩種信號的本質，以及如何在日常生活中使用它們來提高生活品質。
本書的章節是按照作者的理解安排的，你不必按照章節依次閱讀，也不見得要閱讀整本書。第1章主要介紹信號處理如何在近現代變得如此重要及其原因。第2～5章則闡述模擬信號和數字信號的基本性質。其他章節介紹模擬信號和數字信號的處理方法。
全書的內容大致如此。我們希望你能喜歡這本書，還望它能給你帶來幫助。
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
目錄
第1章 什么是數字信號處理 1
幻影技術 1
什么是信號 2
模擬信號和數字信號 3
數字信號處理 3
本章要點 5
第2章 模擬信號 7
什么是模擬信號 7
溫度模擬信號 7
音頻模擬信號 8
電子模擬信號 10
什么是電壓 10
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