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本课件先说明数字信号处理的对象与优势：模拟信号经传感器采集、采样与量化转换为数字信号后由数字滤波器处理；随后讲解低频高频信号、频谱与滤波器系数的含义，最后列举语音识别、音乐处理、调制解调、蜂窝电话与音视频传输中的DSP应用。
数字信号处理：章节封面，标示本章主题与内容范围。
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At the heart of DSP lie the signal stobe processed 3. Signal sarevariations that carry information from one place to another. The outside world, for example, prov ides variation sin pressure or light intensity that human scan perceive. Change sin pressure at the eardrum are heard assounds. Variation sin light intensity att here tina ares eenasimages. These signal sareanalogsignals. They can take any value fro macon tinuumof value san dare define date very instant of time. Sound sareone-dimensional analog sign als:Thesize, or amplitude, of pressure variation schanges with time. As another example, the voltage available fro man electrical outlet in North America variessmoothly from itsminimumtoits maximum andbacktoits minimum again,60 timesper second
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In order to process sign als, they must first becaptured. Sound sign als, for example, are acquire dusinga micro phone, which convert sac oust icsignalsinto electrical sign als. Images, on the other hand, are capture dusingananalogor digital camera. In analog came ras, light sign als control chemical react ionsona photo graphic film. In digital came ras, light sign als from object sin view create charge packet sthatareconvertedinto electrical signal sonatwo-dimensional grid. These electrical signalsare, like the light signal sthatproduced them, ana login nature. Because they carr yin format iona tan infinite number of level sand point sin time, analog signal sarenotsuitedto computer process ing. They must be sample dan dconvertedinto digital form before they can be processed. Digital signal sareperfectly suited for computer process ing because the yare defined aton lya finite number of level sand point sin time
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Both analog and digital signal sarep resent inmost digital process ingsystems. Analog signal sat the in putto the system are converted to digital form for process ing. Afterproces sing, signal sin digital for mare converted back to analog form for output. Itisthe process ing stage, whereon ly digital signal sexist, that the flexibility and speed of DSP are realized. Asystemanalyzes, comb ines, modifies, records, orplaysbacksignals. Anim age compression system, for example, recodesdigita lima gesso they occupy less memory space and therefore take less time to transmit through the Internet. Aspeechre cognition system is designed to understand human speech automatic ally. Adigital filter, to take another example, all ows certain signal frequencies top ass through the system while bloc kin goth ers. For digital sign als, the poss ibilitiesfor process ing are limitless. Any operation that is possible for number sis also possible for digital signal sand with specialized DSP hardware and software, the operation scan occur atli ghtingspeeds
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Digital system shave many advantage sover analog system. Analog system sarecircuitsconstruc ted from hardware component swhose proper tie scan vary quite wide lywithina manufacturer'stole rance 4. The proper tie scan also change with temperature, alter ing the circuit'sbehavior. In contrast 5, digital system sbehaveina predict able, repeatable way. Their behavior is almost complete lyunaffectedby these problems, because itismostly determined by software. For the same reason, digital system saremuch less affected by noise than analog syst ems. In addition, digital system saresmalle rand consume less power than their analog count erparts. Perhaps the great est advantage of digital technology is the flexibility that allow sade sign tobemodifiedbys imply changing afewlinesina program. Most analog redesign involve sbuildingnewcircuits from scratch
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Sight sand sound sfromthe world around us are analog sign als. In order to process these sign als, sensor stun edtothesignals'character isticsmustbe used. Sensor sexist fora vast array ofsignals. Micro phone sarecommonsoundsensors. Change sin light canbecapturedby semi conductor devi ceslikephotodiodes, photo trans istors, or CCD(charge-couple dde vice) chips, whose ability to carry current chan ges with incident light. Temperature can be measured bythermistors, semi conductor devi ces whose resistance chan ges with temperature, orbythermo coup les, consist ing of two dis similar metal sthatreactdifferently totem pera tureanddevelopa voltage difference. Accelerometer sareusedto measure acceleration. Other sensor sin cludestrainsensors, pressure sensors, andflowsensors
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The most common output for all of these sensor sis an electrical signal, voltage or current, proportion alto the signal being measured. It is this analog electrical signal that must be converted in to digital form. The value sthatthe signal may take between its minimum and maximum value sarenot restricted, and the signal has value sate very instant of time
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Analog-to-digital con version occur sintwosteps. The first step is sampling. Sampling instant snormallyoccurat regular interval scalledsamplingperiods. At each sampling point, the analog signal iss amp led, and the value of the signal is held steady until the next sampling point. This process is called sample and hold. The vertical dash edl ines mark the sampling point. Sampling must be fast enough to capture the most rapid change sin the signal being sampled. If sampling is too slow, important signal characteristic scan be lost, aproblem called alias ing. Note that thea ctofsamplingtakesa finite amount of time, called the acquisition time of the sampler
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The second ste pin the con version between an analog signalanda digital signal, which can begin at the completion of sample acquisition, is to quantize and digitize thea nalogva lues. The hold interval norm ally give sample time for this. Ass oonaspossibleafte reach sampling instant, the convert erse lectsthe quantization level that approx imatesthe sample-and-hold value as clos ely as possible and then as sig nsa binary digital code that identifiesthe quantization level. This comp let est he analog-to-digital con version process
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本页为生词与短语（New words and phrases）列表，收录本节出现的专业词汇。
| 英文词条 | 音标 | 中文释义 |
|---|---|---|
| eardrum | [ˈiəˌdrʌm] | 鼓膜，耳膜 |
| variation | [ˌvɛəriˈeiʃən] | 变化，变动(的程度)，(数量，水平等的)变化，变更，变异 |
| retina | [ˈretinə] | 视网膜 |
| continuum | [kənˈtinjuəm] | 连续统一体 |
| instant | [ˈinstənt] | 片刻，顷刻，刹那，瞬间，某一时刻 |
| amplitude | [ˈæmpliˌtu:d,-ˌtju:d] | (声音，无线电波等的)振幅，幅度，广大，广阔，充足，丰富 |
| minimum | [ˈminiməm] | 最低限度，最小量，极小量 |
| maximum | [ˈmæksiməm] | 最大值的，最大量的最大的量，体积，强度等 |
词条按原文「中文释义—音标—英文词条」的顺序识别，如与原件排版不符以课件原图为准。
本页为生词与短语（New words and phrases）列表，收录本节出现的专业词汇。
| 英文词条 | 音标 | 中文释义 |
|---|---|---|
| acoustic | [əˈku:stik] | 声音的，听觉的，原声的，自然声的 |
| predictable | [priˈdiktəbl] | 可预言(预报)的，可预见的，可预料的 |
| affect | [əˈfekt] | 影响，对……有影响，对……起作用 |
| involve | [inˈvɔlv] | 使某事物成为必要条件或结果，需要，使参与，牵涉 |
| scratch | [skrætʃ] | &，抓，搔，删掉 |
| thermocouple | [θə:məuˌkʌpl] | 热电偶 |
| voltage | [ˈvəultidʒ] | 【电】电压，电压量，伏特数•，加速表，加速计，加速仪，过荷指示器 |
| vertical | [ˈvə(r):tik(ə) l] | 垂直的，直立的，竖立的，纵的 |
词条按原文「中文释义—音标—英文词条」的顺序识别，如与原件排版不符以课件原图为准。
本页为生词与短语（New words and phrases）列表，收录本节出现的专业词汇。
| 英文词条 | 音标 | 中文释义 |
|---|---|---|
| acquisition | [ˌækwiˈziʃ(ə) n] | 取得，获得，习得 |
| quantization | [ˌkwɔntaiˈzeiʃən] | 【物】量子化，分层 |
| approximate | [əˈprɔksimət] | 近似的，大概的 |
| binary | [ˈbainəri] | 二，双，复【化】二元的【数】二进制的 |
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Low frequency signal sareconstantorchanges lowly overtime. They appear att hel eft end of the spectrum. High frequency sign als, on the other hand 2, change rapid lywithtime. They appear at the right end of the spectrum
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Digital filter sareno thing more than equation sdefinedbyalistof filter coefficients 4. These equation sformpartofa digital filter program that accept sra wdataasinputand produce sfiltereddataas output. The beauty of such program sis that filter redesign does notrequirea hardware change:Changing filter behavior is accomplished by sim ply changing the list of filter coefficients. Digital filter program scan be implemented on any processor, but the yare implemented most efficient lyon hardware that isspeci ally designed to perform filter ing and other DSP operation sate norm ousspeeds 5. This DSP hardware enable sext rem ely complex task stobeper forme din negligible amount soft ime, which isthereasonitisso often found at the core of computation-intensive applications
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本页为生词与短语（New words and phrases）列表，收录本节出现的专业词汇。
| 英文词条 | 音标 | 中文释义 |
|---|---|---|
| pitch | [pitʃ] | 扔，投，抛，掷 |
| spectrum | [ˈspektrəm] | 【物】谱，光谱，波谱，能谱，质谱 |
| magnitude | [ˈmæɡnitju:d] | 大小，积，广大，巨大，伟大，重大，重要性，量 |
| domain | [dəuˈmein] | (学问，活动等的)领域，范围 |
| choir | [ˈkwaiə(r)] | (教堂，学校的)唱诗班 |
| soprano | [səˈprɑ:nəu] | 【乐】女高音，高音部，女高音歌手，唱最高音者 |
| equation | [iˈkweiʒ(ə) n] | 【数】方程式，等式 |
| enormous | [iˈnɔ:(r) məs] | 巨大的，大量的，庞大的 |
| ely | [iksˈtri:mli] | 极端地，非常地 |
| negligible | [ˈneɡlidʒəb(ə) l] | 可以忽视的，不足取的，很小的，微不足道的 |
词条按原文「中文释义—音标—英文词条」的顺序识别，如与原件排版不符以课件原图为准。
本页为课文注释（Notes），讲解本节难句的句式与翻译处理。
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Large vocab ulariesof continuous speech can be recognized us ing information from digital speech sign als. Most often, speech recognition method sarebase dona spectral analysis ofspeechsounds. Though this analysis can be time-con sum ing 3, fast DSP hardware makesreal-tim ere cog nit iona reality. The lar ger the population of user sofa speech recognizer, the more variable the speech and the more difficult the task. Greater vocabulary size also make sdi scrim ina tionbetweenwords more challenging. The AT&Ttelephonecompanyhas, for sever alyears, use daw ord-spotting technique for it sdi rectory assistance system. Word spotting help sop erato rsrespondmorequicklyby searching for number sand simple word sem bedded in continuous speech and then collat ing basic information about are quest
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Automatic voice recognition for radio control makeshands-free radio use possible injetcockpits, and similar technology allow sha nds-free use of cellular phone sinautomobiles. In complementary technology, advance dspeech synthesis programs generate natural-sounding speech for automobile warnings, telephone information message sand telephone banking. Indeed, advance dmodelsof human speech developed for speech synthesizer shave been used to produce DSP-based hearing aids that aretunedto compensate precis ely for an individual'sspecific hearing deficiencies
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DSP alsomakes contribution sin the area of music and other sou nds. Old recording sof music and audio track scan becleanedup byre moving click ing and buzz ing sound sin the background. Also, the sound sof musical instrument scan be clos ely cop ied for electronic synthesize rs. Combination so factual recording sand mathematic almodels produce high quality synthesis for many instr uments, including piano, violin, and flute
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Fantastic effectsare possible when DSP is app lied to imagery. Image scan be combined, aswhen Forrest Gumpwas digit ally addedtoafilmof President Nixon. Background speck ling can be removed by ave raging several picture soft he same scene. Movement can be detected by subtract ing one image from another of the same scene, highlight ing the place swherethetwoimages differ. Color map scan be altered, and contrast improved
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Incommunications, DSP play sse vera limp ortantroles, particular lyinsupportof cellular pho nes, digital mod ems, and audio and video trans mission techno log ies. Digital cellular telephone use DSP fort womaintasks:to code speech ascompactlyas possible while maintain ing intelligibility, and totransmitcoded speech reliably toareceiveracr ossa wireless radio frequency link 4. Voice cod ing algor it hms, called vocoders, match voice data toamodelof speech that require sonlyafew para met ers. These para met ers are transmitted to the receiver instead of the speech signal, where the parameter sareappliedtothe same model again tore cover area son able copy of the original voice data. Use ofvocodersdecreases dramatic ally the size of the trans mission sneededto support an individual call, providinga commensurate incr ease in the efficiency of the cellular network
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Since radio frequency link scan not support the trans mission of digital data directly, they must employa modulator. In one common scheme, quadrature amplitude modulation(QAM)5, sever albi tsofdigitaldataata time determine the amplitude and phase ofa sine wave that is transmitted int heir place. At the receiver, the amplitude and phase of the received signal are detect edbyade modulator before the original digital data maybe identified. The two main obstacle sto clean trans mission ofacallare signal fad ing and noise. Several str ategiesareusedto mitigate their effects
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For example, error code sthatcanbe checked by the receive rare append edtosome portion soft he transmitted data. Also, para met ers from different block sof speech are inter leave dwithone another tore duce the chance that the integrity of anent ire block will bede stroy edbya single burst of noise. Asa result of noise and fad ing, the received signal maybe quite unlike the transmitted sequence. To assist in signal recovery, akn own pattern ofbitsissometimes sent from the transmitter to the receiver to allow the receiver to estimate the characteristic soft hel ink and therefore have the great est chance of identify ing the bit sin the received signal correct ly
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Modem technology permit computer stocommunicateu sing ordinary telephone line so rte levi sion cable. Many oft heal go rit hms that permit data to be carrie dat very high rate son these media rel yon complex calculation sthatmustbe completed quick lytokeepup within coming data. Digital data must first becodedfor wired trans mission ina manner that giveshigh throughput andre liable detection. Telephone line impair mentslike noise, fading, and crosstalk can, however, introduce derrors. To saver etransmissions, error code scan bead dedtothe transmitted data that permit the receiver notonlyto detect but also tocorrecterrors
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As force llularphones, digital modem ssometimes exchange known signal sto monitor the quality oft hecommunications channel. Some modem scan even adjust their trans mission rate sin accordance with the quality of the line, to help error stoa minimum. In addition toc odin gand error control, modem scan apply compression tore duce thea mount ofdatatobe transmitted. In one compression scheme, for example, short code saresubstituted for the most common bitpatterns, code sthatarere placed by the original pattern sat the receiver. For secure trans missions, somemodems provide encryption capability as well
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Whether trans mission is wire dor wireless, the growth of the Internet hasoccasionedan enormous incr ease in the movement of audio andvideofiles. To save space and also trans mission time, compression str ate gie shave developed far beyond simple substitution alcodes. Video compressions chem esl ike MPEG(moving picture expert sgroup)5, for example, rel yon the fact that neigh boring frame sofa video sequence have very similar content. Instead ofc odin gall pixel sinallfr ames, the difference sbetweenframesarecoded. MPEG also incorporate san audio compression standard, MP 3, which exploit sthecharact eristic soft he human auditory system
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The result sof DSP can bead mire dandenjoyed without any knowledge of the underlying mathematics. Active analysis, filter ing, or trans formation ofsignals does, however, require some understanding ofthemaththatdr ives DSP
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本页为生词与短语（New words and phrases）列表，收录本节出现的专业词汇。
| 英文词条 | 音标 | 中文释义 |
|---|---|---|
| accessible | [əkˈsesəb(ə) l] | 可以进入的，容易理解的，能接近的 |
| cockpit | [ˈkɔkˌpit] | 战场，(戏院的)正厅，(军舰内的)伤兵室 |
| complementary | [ˌkɔmpliˈment(ə) ri] | 补充的，补足的，互补的【生】互配(力)的 |
| synthesizer | [ˈsinθəsaizə(r)] | 合成者，合成物【电】合成器，综合器•，助听器 |
| obstacle | [ˈɔbstək(ə) l] | 障碍(物)，妨害，阻碍，干扰 |
| exchange | [iksˈtʃeindʒ] | 交换，互换 |
| accordance | [əˈkɔ:(r) d(ə) ns] | 一致，协调 |
词条按原文「中文释义—音标—英文词条」的顺序识别，如与原件排版不符以课件原图为准。
本页为生词与短语（New words and phrases）列表，收录本节出现的专业词汇。
| 英文词条 | 音标 | 中文释义 |
|---|---|---|
| adj | [ˌsʌbstiˈtju:ʃənəI] | |
| execute | [ˈeksiˌkju:t] | 实行，实施，执行，履行，贯彻，完成 |
| dimensional | [diˈmenʃənəl] | 尺寸的，空间的 |
| quadrature | [ˈkwɔdrətʃə] | 【物】正交，转象差，九十度相位差 |
| flute | [flu:t] | 【乐】长笛，长笛吹奏者，(风琴的)长笛音 |
| fantastic | [fænˈtæstik] | 空想的，异想天开的 |
| speckle | [ˈspek(ə) l] | 斑点，斑纹，加斑点，玷污，点缀 |
| intelligibility | [inˈtelidʒibiliti] | 可理解性，可理解的事物 |
| vocoder | [vəuˈKəudə] | 〈美〉语音编码机 |
词条按原文「中文释义—音标—英文词条」的顺序识别，如与原件排版不符以课件原图为准。
本页为生词与短语（New words and phrases）列表，收录本节出现的专业词汇。
| 英文词条 | 音标 | 中文释义 |
|---|---|---|
| commensurate | [kəˈmenʃərət] | 相称的，相当的，能通约的，同量的，同样大小的 |
| dramatically | [drəˈmætikli] | 显著地，戏剧地 |
| vocabulary | [vəuˈkæbjuləri] | 词汇，单词集 |
| identify | [aiˈdentifai] | 验明(正身)，鉴别，辨认，识别 |
| calculation | [ˌkælkjuˈleiʃ(ə) n] | 计算，计算法，推定，预测 |
| encryption | [inˈkripʃən] | 【计】加密 |
词条按原文「中文释义—音标—英文词条」的顺序识别，如与原件排版不符以课件原图为准。
本页为课文注释（Notes），讲解本节难句的句式与翻译处理。
本页英文原文由图片提取，部分单词之间空格缺失，已按大小写与标点边界补回分隔，确切分词请以课件原图为准。
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