Transcript DSP - 上海海事大学信息工程学院

Unit 6 Introduction to
Digital Signal
Processing
Background
Words and expressions
Text and notes
Grammar
Exercises
Reading material
上海海事大学信息工程学院
Background
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Introduction to Digital Signal Processing
What is DSP?
DSP, or Digital Signal Processing, as the term suggests, is the
processing of signals by digital means. A signal in this context can
mean a number of different things. Historically the origins of signal
processing are in electrical engineering, and a signal here means an
electrical signal carried by a wire or telephone line, or perhaps by a
radio wave. More generally, however, a signal is a stream of
information representing anything from stock prices to data from a
remote-sensing satellite. The term "digital" comes from "digit",
meaning a number (you count with your fingers - your digits), so
"digital" literally means numerical; the French word for digital is
numerique. A digital signal consists of a stream of numbers, usually
(but not necessarily) in binary form. The processing of a digital
signal is done by performing numerical calculations.
Background
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Analog and digital signals
In many cases, the signal of interest is initially in the form of an
analog electrical voltage or current, produced for example by a
microphone or some other type of transducer. In some situations,
such as the output from the readout system of a CD (compact disc)
player, the data is already in digital form. An analog signal must be
converted into digital form before DSP techniques can be applied.
An analog electrical voltage signal, for example, can be digitised
using an electronic circuit called an analog-to-digital converter or
ADC. This generates a digital output as a stream of binary numbers
whose values represent the electrical voltage input to the device at
each sampling instant.
Background
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Signal processing
Signals commonly need to be processed in a variety of
ways. For example, the output signal from a transducer
may well be contaminated with unwanted electrical
"noise". The electrodes attached to a patient's chest
when an ECG is taken measure tiny electrical voltage
changes due to the activity of the heart and other
muscles. The signal is often strongly affected by "mains
pickup" due to electrical interference from the mains
supply. Processing the signal using a filter circuit can
remove or at least reduce the unwanted part of the
signal. Increasingly nowadays, the filtering of signals to
improve signal quality or to extract important information
is done by DSP techniques rather than by analog
electronics.
Background
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Development of DSP
The development of digital signal processing dates from
the 1960's with the use of mainframe digital computers
for number-crunching applications such as the Fast
Fourier Transform (FFT), which allows the frequency
spectrum of a signal to be computed rapidly. These
techniques were not widely used at that time, because
suitable computing equipment was generally available
only in universities and other scientific research
institutions.
Background
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Digital Signal Processors (DSPs)
The introduction of the microprocessor in the late 1970's
and early 1980's made it possible for DSP techniques to
be used in a much wider range of applications. However,
general-purpose microprocessors such as the Intel x86
family are not ideally suited to the numerically-intensive
requirements of DSP, and during the 1980's the
increasing importance of DSP led several major
electronics manufacturers (such as Texas Instruments,
Analog Devices and Motorola) to develop Digital Signal
Processor chips - specialised microprocessors with
architectures designed specifically for the types of
operations required in digital signal processing.
Background
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(Note that the acronym DSP can variously mean Digital
Signal Processing, the term used for a wide range of
techniques for processing signals digitally, or Digital
Signal Processor, a specialised type of microprocessor
chip). Like a general-purpose microprocessor, a DSP is
a programmable device, with its own native instruction
code. DSP chips are capable of carrying out millions of
floating point operations per second, and like their betterknown general-purpose cousins, faster and more
powerful versions are continually being introduced.
DSPs can also be embedded within complex "systemon-chip" devices, often containing both analog and
digital circuitry.
Background
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Applications of DSP
DSP technology is nowadays commonplace in such
devices as mobile phones, multimedia computers, video
recorders, CD players, hard disc drive controllers and
modems, and will soon replace analog circuitry in TV
sets and telephones. An important application of DSP is
in signal compression and decompression. Signal
compression is used in digital cellular phones to allow a
greater number of calls to be handled simultaneously
within each local "cell". DSP signal compression
technology allows people not only to talk to one another
but also to see one another on their computer screens,
using small video cameras mounted on the computer
monitors, with only a conventional telephone line linking
them together. In audio CD systems, DSP technology is
used to perform complex error detection and correction
on the raw data as it is read from the CD.
Background
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Although some of the mathematical theory underlying
DSP techniques, such as Fourier and Hilbert
Transforms, digital filter design and signal compression,
can be fairly complex, the numerical operations required
actually to implement these techniques are very simple,
consisting mainly of operations that could be done on a
cheap four-function calculator. The architecture of a DSP
chip is designed to carry out such operations incredibly
fast, processing hundreds of millions of samples every
second, to provide real-time performance: that is, the
ability to process a signal "live" as it is sampled and then
output the processed signal, for example to a
loudspeaker or video display. All of the practical
examples of DSP applications mentioned earlier, such
as hard disc drives and mobile phones, demand realtime operation.
Background
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The major electronics manufacturers have
invested heavily in DSP technology.
Because they now find application in
mass-market products, DSP chips account
for a substantial proportion of the world
market for electronic devices. Sales
amount to billions of dollars annually, and
seem likely to continue to increase rapidly.
DSP芯片制造商
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德州仪器(Texas Instruments)，简称TI，是全
球领先的半导体公司，为现实世界的信号处理
提供创新的数字信号处理(DSP)及模拟技术。
除半导体业务外，还提供包括教育技术和数字
光源处理解决方案(DLP)。TI总部位于美国得克
萨斯州的达拉斯，并在25多个国家设有制造、
设计或销售机构。
DSP芯片制造商
亚德诺半导体
 www.Analog.com
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Morse code
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http://en.wikipe
dia.org/wiki/Mo
rse_code
Reed-Solomon code
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In coding theory, Reed–Solomon (RS) codes are linear error-correcting
codes notably invented by and named after Irving S. Reed and Gustave
Solomon. Reed-Solomon error correction works by oversampling a
polynomial constructed from the data. The polynomial is evaluated at
several points, and these values are sent or recorded. Sampling the
polynomial more often than is necessary makes the polynomial overdetermined. As long as it receives "many" of the points correctly, the
receiver can recover the original polynomial even in the presence of a "few"
bad points.
RS codes have important applications from deep-space communication to
consumer electronics, and are prominently used in CDs, DVDs, Blu-ray
Discs(蓝光光盘), in data transmission technologies such as DSL & WiMAX,
in broadcast systems such as DVB and ATSC, and in computer applications
such as RAID 6 systems.
上海海事大学信息工程学院
Words and expressions
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Adjacent
Alphabetical
Avalanche
Binary
Discretize
Disturbance
Fuzzy
Interdisciplinary
Multiplexing
Numeral
Oscilloscope
Overlapping
Perturbation
Quantization
Resonance
Round
adj.
adj.
n.
adj.
vt.
n.
adj.
adj.
n.
n.
n.
n.
n.
n.
n.
v.
邻近的，接近的
以字母顺序的，字母的
雪崩
二进位的，二元的
使离散
干扰，打扰，骚乱，扰动
模糊的，失真的
跨学科的
多路技术
数字
示波器
重叠
微扰，摄动
量化
谐振，共振
四舍五入
上海海事大学信息工程学院
Words and expressions
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Synthesize
v. 综合，合成
Truncation
n. 截断
Versatile
adj. 通用的，万能的，多才多艺的
Vibratory
adj. 振动的，振动性的
Vocal
adj. 发嗓音的，声音的，有声的，歌唱的
Decimal part
小数部分
Sign-and-magnitude coding
符号数值编码
CD (compact Disc)
光盘
LSB (Least significant bit)
最低有效位
MSB (Most significant bit)
最高有效位
Radar (Radio detective and ranging) 雷达，电波探测器
Sonar (Sound detective and ranging) 声纳，声波探测器
上海海事大学信息工程学院
Text and notes
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This type of representation, however, is
not used because it is susceptible to noise,
shifting of power supply, and any other
disturbances.
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不过，由于这种表示法易受噪声、电源起
伏及其他干扰的影响而未予采用。
上海海事大学信息工程学院
Text and notes
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To process an analog signal digitally, it
must first be discretized in time to yield a
discrete-time signal and then quantized in
amplitude to yield a digital signal.
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要以数字化的方式处理模拟信号，应先对
模拟信号在时间上离散化以产生离散时间
信号，然后对其幅值量化以产生数字信号。
上海海事大学信息工程学院
Text and notes
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In quantization, if the amplitude of a discretetime signal does not fall exactly on a
quantization level, then the value must be
approximated by a quantization level either by
truncation or rounding; in either case, errors will
occur.
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量化时，如果离散时间信号的幅度与量化电平不
一致，那么就应采用截断或四舍五入的方式将它
近似为某个量化电平，两种情形都会产生误差。
上海海事大学信息工程学院
Text and notes
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For convenience, we use digital signals and
discrete-time signals interchangeably with the
understanding that all DT signals must be
transformed into digital signals in
implementation and all digital signals are
considered as DT signals in analysis and design.
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由于在电路实现时必须将离散时间信号转换为数
字信号，而在分析与设计过程中则将数字信号看
作是离散时间信号，为方便起见，我们不加区别
的使用数字信号与离散时间信号。
上海海事大学信息工程学院
Text and notes
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Another example is the transmission of the
pictures of the Mars, taken by a spacecraft,
to the ground station on the earth.
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另一个例子就是将由太空船拍摄的火星图
片传至地球上的地面工作站。
上海海事大学信息工程学院
Text and notes
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The roots of DSP are in the 1960s and
1970s when digital computers first became
available.
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数字信号处理始于二十世纪六七十年代，
当时计算机刚问世。
上海海事大学信息工程学院
Applications of DSP
上海海事大学信息工程学院
Applications of DSP
上海海事大学信息工程学院
Applications of DSP
上海海事大学信息工程学院
Digital Signal Processing
Best digital signal processing books:
 http://www.dspguru.com/info/books/favor2.
htm
 Digital Signal Processing: A Computer
Science Perspective:
http://www.dspcsp.com/
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上海海事大学信息工程学院
Grammar－动词非谓语形式
如前所述，科技文章要求行文简练，结构紧凑，
为此：
 使用分词短语代替定语从句或状语从句；
 使用分词独立结构代替状语从句或并列分句；
 使用不定式短语代替各种从句；
 介词加动名词短语代替定语从句或状语从句。
 这样可以缩短句子，又比较醒目 。
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上海海事大学信息工程学院
Grammar－动词非谓语形式
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1、动名词
动名词以名词为主，可充当主语、宾语、宾语补足语、表
语以及定语，同时保留动词性，可带宾语和状语。动名词
名词性较强，表示经常性动作。
Selecting a desired signal is one of three important
functions performed by the tuning circuit.
This reliability can further be improved by using errordetecting and error-correcting codes.
One of the greatest advantages of the transistor is its
being able to be made very small.
上海海事大学信息工程学院
Grammar－动词非谓语形式
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2、现在分词
现在分词以形容词、副词为主，保留动作性，可
作定语、状语用，现在分词具有主动和进行的意
义。
In the process of transmission, the signals
bearing the information are contaminated by
noise.
注：动名词做主语时，动名词和其所修饰的词没
有逻辑上的主谓关系，而分词做定语时，分词和
其所修饰的词有逻辑上的主谓关系。
上海海事大学信息工程学院
Grammar－动词非谓语形式
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The left-most bit, excluding the sign bit, is the most
significant bit (MSB) and the right-most bit is the least
significant bit (LSB). (主语补足语)
Using time multiplexing, a digital system can be used
to process a number of digital signals.(方式状语)
Physically, the transistor consists of three parts, emitter,
base and collector, the base region being very thin.
(分词独立结构，做状语，逻辑主语与句子的主语不一致)
This article deals with microwaves, with particular
attention being paid to radio location. (分词复合结构，
with/without+名词＋分词)
上海海事大学信息工程学院
Grammar－动词非谓语形式
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3、过去分词
过去分词同现在分词一样，以形容词、副词为主，
也保留了动词性，只作定语、状语，含有被动和
完成的意义。
Messages sent by telegraph are digital signals.
Given a pattern, its recognition/classification
may consist of one the following two tasks:
supervised classification or unsupervised
classification.
上海海事大学信息工程学院
Grammar－动词非谓语形式
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4、不定式
不定式兼有名词、形容词、副词，保留了动词性，可用做
定语、状语、表语、主语和宾语，常表示具体的一次性动
作。
If you want to specialize in DSP, these are the allied
areas you will also need to study.
The only convenient way to store analog signals is to
tape or film them.
除way外，要求不定式做定语的名词有：ability, power,
tendency, capacity, reason, chance, time, method,
attempt, opportunity, thing, work, property.
上海海事大学信息工程学院
Grammar－动词非谓语形式
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In analog systems, it is difficult or very expensive to have
a number of components with identical value.
To simplify the discussion, we use decimal numbers to
illustrate this point.
In some filter design problems, a primary objective may
be to control some aspect of the time response such as
the impulse response or the step response.
注：常用的主语有以下名词：aim, task, duty, goal,
work, job, role, problem, mistake etc.
上海海事大学信息工程学院
常用写作句型
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5.
毫无疑问……
There is no doubt that……
There is no question that……
Without doubt (question), ……
Beyond doubt (question), ……
No (out of ) doubt, ……
上海海事大学信息工程学院
句子练习
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根据上面的实验结果，毫无疑问，A教授提
出的新算法性能更好。
上海海事大学信息工程学院
听力练习
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4D打印机的诞生
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使用石墨烯：5分钟即可充满电的超级充电
宝
上海海事大学信息工程学院
Exercises
1. Choose the best answer for each of the
following questions.
(1) By using the sign-and-magnitude coding scheme, the
binary sequence 1101.01 represents decimal number
with its value equal to _____.
b
a. 6.25
b. -5.25
c. 4.25
d. -3.25
上海海事大学信息工程学院
Exercises
1. Choose the best answer for each of the
following questions.
(2) The first step to process an analog signal digitally is to
c
_____.
a. encode it by using the binary coding scheme
b. quantize it in amplitude
c. sample it an discrete time instant
d. pass it through a D/A converter
上海海事大学信息工程学院
Exercises
1. Choose the best answer for each of the
following questions.
(3) The following descriptions about quantization errors are
b
correct except ______.
a. quantization errors occur when the amplitude of a discretetime signal is not identical to the quantization level
b. the study of quantization errors is not important
c. quantization errors can be ignored if the DSP processors
have a large number of bits
d. quantization errors are always smaller than the
quantization interval between adjacent quantization levels
上海海事大学信息工程学院
Exercises
1. Choose the best answer for each of the
following questions.
(4) Regarding the advantages of digital techniques over the
analog ones, which one of the following is not
mentioned: _____.
a
a. The transmission of analog signals is more costly than
that of digital ones
b. The precision in digital techniques is much higher than
that in analog techniques
c. Digital techniques are less sensible to small noise and
disturbances
d. It is much easier to store a digital signal than an
analog one
上海海事大学信息工程学院
Exercises
1. Choose the best answer for each of the
following questions.
(5) The application areas of DSP include the following but
b
_____.
a. earthquake recording & analysis
b. cognitive science
c. echo reduction
d. simulation and modeling
上海海事大学信息工程学院
Exercises
2. Substitute the underlining words with the
most appropriate choices.
(1) Each bit occupies approximately a distance of 1
micrometer. C（b）
_____
a. takes over
b. takes up
c. keeps in
d. keep up
上海海事大学信息工程学院
Exercises
2. Substitute the underlining words with the
most appropriate choices.
(2) If the signal is transmitted by analog techniques, the
received signal will be severely corrupted by noise, and
It is not possible to reconstruct the picture. _____
d
a. influenced
b. affected
c. combined
d. contaminated
上海海事大学信息工程学院
Exercises
2. Substitute the underlining words with the
most appropriate choices.
(3) In digital display, digital signals can easily be frozen,
a
expanded, and manipulated. _____
a. maneuvered
b. processed
c. analyzed
d. altered
上海海事大学信息工程学院
Exercises
2. Substitute the underlining words with the
most appropriate choices.
(4) Rather than being motivated by military and government
needs, DSP was suddenly driven by the commercial
a
marketplace. _____
a. In stead of
b. So long as
c. While
d. Upon
上海海事大学信息工程学院
Exercises
2. Substitute the underlining words with the
most appropriate choices.
(5) This fact speeds considerably the spreading of digital
c
techniques. _____
a. velocity
b. accelerates
c. fast
d. impulses
上海海事大学信息工程学院
Exercises
2. Substitute the underlining words with the
most appropriate choices.
(6) DSP is very interdisciplinary, relying on the technical
d
work in many adjacent fields. _____
a. different
b. same
c. similar
d. neighboring
上海海事大学信息工程学院
Exercises
3. Translate the following sentences into
Chinese.
(1) More generally, signal processing is an operation
designed for extracting, enhancing storing, and transmitting useful information. The distinction between useful
and unwanted information is often subjective as well as
objective.
(2) System using the DSP approach can be
developed using software running on a general-purpose
computer. Therefore DSP is relatively convenient to
develop and test, and the software is portable.
上海海事大学信息工程学院
Exercises
3. Translate the following sentences into
Chinese.
(3) Digital signal processing generally approaches
the problem of voice recognition in two steps: feature
extraction followed by feature matching.
(4) The Fourier decomposition is the basis for a
broad and powerful area of mathematics called Fourier
analysis, and the even more advanced Laplace and ztransforms. Most cutting-edge DSP algorithms are based
on some aspect of these techniques.
上海海事大学信息工程学院
Exercises
3. Translate the following sentences into
Chinese.
(5) DSP is the mathematics, the algorithms, and the
techniques used to manipulate real world signals after
they have been converted into a digital form. This
includes a wide variety of goals, such as: enhancement
of visual images, recognition and generation of speech,
compression of data for storage and transmission, etc.
(6) A basic premise of this book is that most practical
DSP techniques can be learned and used without the
traditional barriers of detailed mathematics and theory.
上海海事大学信息工程学院
Exercises
4. Fill in blanks with appropriate form of the
verbs shown in the parentheses.
Echoes are a series problem in long distance tele-phone
connections. When you speak into a telephone, a signal
___________(represent)
your voice travels to the
representing
returns
connecting receiver, where a portion of it ______(return)
as an echo. If the connection is within a few hundred
elapsed
miles, the _______(elapse)
time for receiving the echo is
only a few milliseconds. The human ear is accustomed
to ______(hear)
echoes with these small time delays,
hearing
and the connection sounds quite normal. As the
上海海事大学信息工程学院
Exercises
4. Fill in blanks with appropriate form of the
verbs shown in the parentheses.
distance becomes large, the echo becomes increasingly
noticeable and _______(irritate).
The delay can be
irritating
several hundred milliseconds for intercontinental
communications, and ___(be)
particularly objectionable.
is
DSP attacks this type of problem by measuring the
generating
returned signal and _________(generate)
an appropriate
antisignal ________(cancel)
the offending echo. This
to cancel
same technique allows speakerphone users to hear and
speak at the same time without fighting audio feedback
上海海事大学信息工程学院
Exercises
4. Fill in blanks with appropriate form of the
verbs shown in the parentheses.
(squealing). It can also be used to reduce environmental
noise by canceling it with digitally generated
________(generate)
antinoise.
Another interesting DSP application is artificial
reverberation in music preparation. If the individual
channels are simple added together, the resulting piece
______(sound) frail and diluted. This is because
sounds
listeners ____________(influence)
by the echo or
are influenced
reverberation content of the music, which is usually
上海海事大学信息工程学院
Exercises
4. Fill in blanks with appropriate form of the
verbs shown in the parentheses.
minimized in the sound studio. DSP allows artificial
be added
echoes and reverberation to
__________(add)
during mix
down to simulate various ideallistening
_______(listen)
environments. Echoes with delays of a few hundred
milliseconds give the impression of cathedral like
Adding
location. ______(add)
echoes with delays of 10-20
milliseconds provide the perception of more modest size
listening rooms.
上海海事大学信息工程学院
Reading material
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2.
3.
4.
5.
Data Compression Standards
Five parts:
MPEG-1
MPEG-2
MPEG-4
MPEG-7
MPEG-21
上海海事大学信息工程学院
New Words
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Artifact
人造物品
Chart
制图
Entropy
熵
Interleave
交错
Mold
模型
Protocol
协议
UNICODE
统一的字符编码标准，采用双字节对字符进行编码
Intellectual property 知识产权
ASCII (American Standard Code for Information Interchange)
美国信息交换标准码
DCT
离散余弦变换
MPEG (Moving Picture Expert Group) 运动图像专家组，一种压缩比
率较大的移动图像和声音的压缩标准
VLC (Variable length coding) 可变长编码
上海海事大学信息工程学院
Assignment
Do exercises 1,2 ,3 and 4 in page 81;
 Read the reading material.
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上海海事大学信息工程学院
Further reading material
Yuhong Liu and Yan Sun, IEEE Signal
Processing Magazine, 149-156, 2014
 Securing Digital Reputation in Online
Social Media
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上海海事大学信息工程学院