數(shù)字信號(hào)處理外文翻譯

1、<p>　　畢業(yè)設(shè)計(jì)(論文)外文資料翻譯</p><p>　　專 業(yè)： 自動(dòng)化 </p><p>　　姓 名： </p><p>　　學(xué) 號(hào)： </p><p>　　外文題目： The Breadth and Depth of DSP

2、 </p><p>　　外文出處：The Scientist and Engineer's Guide to DSP </p><p>　　1 DSP的廣度和深度</p><p>　　數(shù)字信號(hào)處理是最強(qiáng)大的技術(shù)，將塑造二十一世紀(jì)的科學(xué)與工程之一。革命性的變化已經(jīng)在廣泛的領(lǐng)域：通信，醫(yī)療成像，雷達(dá)和聲納，高保真音樂(lè)再現(xiàn)，石油勘探，僅舉幾例。上述各領(lǐng)域已建立了

3、深厚的DSP技術(shù)，用自己的算法，數(shù)學(xué)，和專門技術(shù)。這種呼吸和深度的結(jié)合，使得它不可能為任何一個(gè)人掌握所有已開(kāi)發(fā)的DSP技術(shù)。 DSP教育包含兩個(gè)任務(wù)：學(xué)習(xí)一般適用于作為一個(gè)整體領(lǐng)域的概念，并學(xué)習(xí)您感興趣的特定領(lǐng)域的專門技術(shù)。本章開(kāi)始描述DSP已在幾個(gè)不同領(lǐng)域的戲劇性效果的數(shù)字信號(hào)處理的世界，我們的旅程。革命已經(jīng)開(kāi)始。</p><p>　　1.1 DSP的根源</p><p>　　獨(dú)特的數(shù)據(jù)

4、類型，它使用的信號(hào)，數(shù)字信號(hào)處理是區(qū)別于其他計(jì)算機(jī)科學(xué)領(lǐng)域。在大多數(shù)情況下，這些信號(hào)源于感覺(jué)來(lái)自現(xiàn)實(shí)世界的數(shù)據(jù)：地震的震動(dòng)，視覺(jué)圖像，聲波等DSP是數(shù)學(xué)，算法，并用來(lái)操縱這些信號(hào)的技術(shù)后，他們已被轉(zhuǎn)換成數(shù)字形式。這包括了各種目標(biāo)，如：加強(qiáng)視覺(jué)圖像識(shí)別和語(yǔ)音生成，存儲(chǔ)和傳輸?shù)臄?shù)據(jù)壓縮，等假設(shè)我們重視計(jì)算機(jī)模擬 - 數(shù)字轉(zhuǎn)換器，并用它來(lái)獲得一個(gè)現(xiàn)實(shí)世界的數(shù)據(jù)塊。 DSP回答了這個(gè)問(wèn)題：下一步怎么辦？</p><p>

5、　　DSP的根是在20世紀(jì)60年代和70年代數(shù)字計(jì)算機(jī)時(shí)首次面世。電腦是昂貴的，在這個(gè)時(shí)代，DSP是有限的，只有少數(shù)關(guān)鍵應(yīng)用。努力開(kāi)拓，在四個(gè)關(guān)鍵領(lǐng)域：雷達(dá)和聲納，國(guó)家安全風(fēng)險(xiǎn)是石油勘探，可以大量資金;太空探索，其中的數(shù)據(jù)是不可替代的;和醫(yī)療成像，可節(jié)省生活。 20世紀(jì)80年代和90年代的個(gè)人電腦革命，引起新的應(yīng)用DSP的爆炸。而不是由軍方和政府的需求動(dòng)機(jī)，DSP的突然被帶動(dòng)的商業(yè)市場(chǎng)。任何人士如認(rèn)為他們可以使資金在迅速擴(kuò)大的領(lǐng)域突然一

6、個(gè)DSP供應(yīng)商。 DSP的市民等產(chǎn)品達(dá)到：移動(dòng)電話機(jī)，光盤播放器，電子語(yǔ)音郵件。</p><p>　　這一技術(shù)革命，從自上而下的發(fā)生。在20世紀(jì)80年代初，DSP是研究生水平的課程，在電氣工程教授。十年后，DSP已成為標(biāo)準(zhǔn)的本科課程的一部分。今天，DSP是一種在許多領(lǐng)域的科學(xué)家和工程師所需要的基本技能。作為一個(gè)比喻，DSP可以比以前的技術(shù)革命：電子。雖然仍是電氣工程領(lǐng)域，幾乎所有的科學(xué)家和工程師有一些基本的電路設(shè)

7、計(jì)的背景。沒(méi)有它，他們將失去在科技世界。 DSP具有相同的未來(lái)。</p><p>　　這最近的歷史是超過(guò)了好奇，它有一個(gè)巨大的影響你的學(xué)習(xí)能力和使用DSP。假設(shè)你遇到一個(gè)DSP的問(wèn)題，并把課本或其他出版物，以找到一個(gè)解決方案。你通常會(huì)發(fā)現(xiàn)什么是頁(yè)后頁(yè)方程，模糊的數(shù)學(xué)符號(hào)，不熟悉的術(shù)語(yǔ)。這是一場(chǎng)惡夢(mèng)！ DSP的文獻(xiàn)多是令人費(fèi)解，甚至在該領(lǐng)域經(jīng)驗(yàn)豐富的。這并不是說(shuō)有什么錯(cuò)用這種材料，它只是一個(gè)非常特殊的觀眾。國(guó)家的最

8、先進(jìn)的研究人員需要這種詳細(xì)的數(shù)學(xué)理解的工作的理論意義。</p><p>　　這本書的一個(gè)基本前提是，可以學(xué)到最實(shí)用的DSP技術(shù)，并沒(méi)有詳細(xì)的數(shù)學(xué)和理論的傳統(tǒng)障礙?？茖W(xué)家和工程師的數(shù)字信號(hào)處理指南是寫給那些想要使用DSP作為一種工具，而不是一個(gè)新的職業(yè)生涯。</p><p>　　本章的其余部分說(shuō)明，其中DSP已經(jīng)產(chǎn)生了革命性的變化的地區(qū)。當(dāng)你通過(guò)每個(gè)應(yīng)用程序，請(qǐng)注意，DSP是非?？鐚W(xué)科，依托

9、在許多相鄰領(lǐng)域的技術(shù)工作。正如圖。如果你想專注于DSP，這是多領(lǐng)域，則還需要研究。</p><p><b>　　1.2 通信</b></p><p>　　通信是信息傳輸從一個(gè)位置到另一個(gè)。這包括各種形式的信息：電話交談，電視信號(hào)，計(jì)算機(jī)中的文件，和其他類型的數(shù)據(jù)。傳輸信息，你需要在兩個(gè)地點(diǎn)之間的通道。這可能是一個(gè)線對(duì)無(wú)線電信號(hào)，光纖等電信公司接收他們的客戶的信息轉(zhuǎn)移支

10、付，而他們一定要以建立和維護(hù)渠道。金融的底線很簡(jiǎn)單：信息越多，他們可以通過(guò)一個(gè)單一的通道，他們更多的錢。 DSP已徹底改變電信業(yè)在許多領(lǐng)域：信號(hào)音的產(chǎn)生和檢測(cè)，頻帶的轉(zhuǎn)移，過(guò)濾，除去電源線的嗡嗡聲，從電話網(wǎng)絡(luò)等具體的例子將在這里討論：復(fù)用，壓縮和回聲控制。</p><p><b>　　1.2.1 復(fù)用</b></p><p>　　在世界上大約有10億電話。在按幾個(gè)按鈕

11、，開(kāi)關(guān)網(wǎng)絡(luò)允許其中任何一項(xiàng)，只有幾秒鐘的任何其他連接。這項(xiàng)任務(wù)的艱巨，是超乎想象！直到20世紀(jì)60年代，兩個(gè)電話之間的連接需要通過(guò)機(jī)械開(kāi)關(guān)和放大器的模擬語(yǔ)音信號(hào)。一個(gè)連接需要一對(duì)導(dǎo)線。相比之下，DSP音頻信號(hào)轉(zhuǎn)換成串行數(shù)字?jǐn)?shù)據(jù)流。由于位可以輕松地交織在一起，后來(lái)分開(kāi)，很多電話交談可以傳輸渠道單一。例如，一個(gè)電話標(biāo)準(zhǔn)，被稱為T載波系??統(tǒng)可以同時(shí)傳送24個(gè)語(yǔ)音信號(hào)。每個(gè)語(yǔ)音信號(hào)進(jìn)行采樣，每秒8000次，使用一個(gè)8位集成的（對(duì)數(shù)壓縮）模擬到

12、數(shù)字的轉(zhuǎn)換。這個(gè)結(jié)果在64,000比特/秒，所有24個(gè)被包含在1.544兆比特/秒的渠道代表每個(gè)語(yǔ)音信號(hào)。這個(gè)信號(hào)可以傳輸，使用普通電話線，22號(hào)銅線，一個(gè)典型的互連距離約6000英尺。數(shù)字傳輸?shù)馁Y金優(yōu)勢(shì)是巨大的。線和模擬開(kāi)關(guān)是昂貴的數(shù)字邏輯門價(jià)格便宜。</p><p><b>　　1.2.2 壓縮</b></p><p>　　當(dāng)語(yǔ)音信號(hào)數(shù)字化，在8000樣本/秒，大

13、多數(shù)的數(shù)字信息是多余的。也就是說(shuō)，任何一個(gè)樣本進(jìn)行信息主要由鄰近的樣品重復(fù)。 DSP算法已發(fā)展到幾十個(gè)數(shù)字化語(yǔ)音信號(hào)轉(zhuǎn)換成數(shù)據(jù)流，需要較少的比特/秒。這些被稱為數(shù)據(jù)壓縮算法。匹配解壓縮算法，用于恢復(fù)其原來(lái)的形式的信號(hào)。這些算法不同的金額達(dá)到壓縮和音質(zhì)。在一般情況下，減少64千比特/秒的數(shù)據(jù)傳輸速率為32千比特/秒的結(jié)果，在不損失音質(zhì)。當(dāng)壓縮到8千比特/秒的數(shù)據(jù)傳輸速率，聲音明顯受到影響，但仍然可用的長(zhǎng)途電話網(wǎng)絡(luò)。達(dá)到的最高壓縮約2千比特

14、/秒，高度扭曲的聲音，但可用于某些應(yīng)用，如軍事和海底通信。</p><p><b>　　1.2.3 回聲</b></p><p>　　控制回聲是一個(gè)嚴(yán)重的問(wèn)題，在長(zhǎng)途電話連接。當(dāng)你走進(jìn)一個(gè)電話，你的聲音信號(hào)傳播連接的接收器，它的一部分返回的回聲。如果連接是幾百公里內(nèi)，接收回聲所用的時(shí)間只有幾毫秒。人類的耳朵習(xí)慣于聽(tīng)到這些小的時(shí)間延遲的回聲，連接聽(tīng)起來(lái)很正常。隨著距離變

15、大，回聲變得越來(lái)越明顯和刺激性。延遲是幾百毫秒洲際通信，特別是反感。數(shù)字信號(hào)處理攻擊這類型的問(wèn)題，通過(guò)測(cè)量返回信號(hào)，并產(chǎn)生適當(dāng)?shù)姆葱盘?hào)取消違規(guī)回聲。同樣的技術(shù)，允許免提電話用戶聽(tīng)取和不戰(zhàn)而音頻反饋（嘯）在同一時(shí)間發(fā)言。它也可用于減少環(huán)境噪聲，取消它與數(shù)字產(chǎn)生抗噪。</p><p><b>　　1.3 音頻處理</b></p><p>　　主要的兩個(gè)人的感官是視覺(jué)和聽(tīng)覺(jué)

16、。相應(yīng)地，許多DSP的有關(guān)圖像和音頻處理。人們聽(tīng)音樂(lè)和語(yǔ)音。 DSP已經(jīng)在這兩個(gè)領(lǐng)域取得了革命性的變化。</p><p><b>　　1.3.1 音樂(lè)</b></p><p>　　從音樂(lè)家的麥克風(fēng)，高保真的揚(yáng)聲器的路徑是相當(dāng)長(zhǎng)。數(shù)字?jǐn)?shù)據(jù)表示，重要的是要防止通常與模擬存儲(chǔ)和操作相關(guān)的退化。這是非常熟悉的人與光盤，錄音帶的音樂(lè)素質(zhì)。在一個(gè)典型的場(chǎng)景，音樂(lè)作品在多個(gè)頻道或曲

17、目的錄音室錄制。在某些情況下，這甚至涉及個(gè)別樂(lè)器和歌手分別記錄。這樣做是為了給錄音師更大的靈活性，創(chuàng)造的最終產(chǎn)品。被稱為復(fù)雜的過(guò)程，結(jié)合到最終產(chǎn)品的個(gè)別曲目的縮混。 DSP可以在組合提供幾個(gè)重要的功能，包括：過(guò)濾，加法和減法信號(hào)，信號(hào)的編輯，等等。</p><p>　　最有趣的音樂(lè)準(zhǔn)備的DSP應(yīng)用之一是人工混響。如果各個(gè)渠道的簡(jiǎn)單相加，導(dǎo)致一塊聽(tīng)起來(lái)體弱及攤薄，音樂(lè)家多，如果在戶外玩耍。這是因?yàn)槁?tīng)眾都深受影響的音

18、樂(lè)，通常是在錄音室最小的回聲或混響內(nèi)容。 DSP允許人造回聲和混響加在混合模擬各種理想的聽(tīng)音環(huán)境。幾百毫秒延遲的回聲，給像位置的大教堂的印象。 10-20毫秒的延遲添加回聲提供更多的適度規(guī)模聆聽(tīng)室的看法。</p><p>　　1.3.2 語(yǔ)音生成</p><p>　　語(yǔ)音生成和識(shí)別被用于人類和機(jī)器之間的溝通。而不是用你的雙手和眼睛，你用你的嘴和耳朵。當(dāng)你的手和眼睛應(yīng)做別的東西，如：駕駛汽車

19、，進(jìn)行手術(shù)，或不幸敵人發(fā)射你的武器，這是非常方便。兩種方法用于計(jì)算機(jī)生成的講話：數(shù)碼錄音和聲道模擬。在數(shù)碼錄音，一個(gè)人的揚(yáng)聲器的聲音數(shù)字化處理和儲(chǔ)存，通常在壓縮形式。在播放過(guò)程中，存儲(chǔ)的數(shù)據(jù)壓縮和轉(zhuǎn)換成模擬信號(hào)。整個(gè)小時(shí)的錄音講話要求只有約3兆字節(jié)的存儲(chǔ)空間，即使是小規(guī)模的計(jì)算機(jī)系統(tǒng)內(nèi)的功能。這是今天使用的數(shù)字語(yǔ)音代最常用的方法。</p><p>　　聲道模擬器比較復(fù)雜，試圖模仿人類創(chuàng)造講話的物理機(jī)制。人類聲道是

20、聲腔與商會(huì)的大小和形狀確定的共振頻率。聲音源于聲道聲和摩擦音，在兩種基本方式之一。濁音，聲帶振動(dòng)產(chǎn)生周期脈沖附近的空氣進(jìn)入聲樂(lè)腔。相比之下，摩擦音源于在嘈雜的空氣湍流，如牙齒和嘴唇，窄縊。聲道模擬器操作產(chǎn)生類似于激??發(fā)這兩種類型的數(shù)字信號(hào)。共鳴腔的特點(diǎn)是通過(guò)類似共振的激勵(lì)信號(hào)，通過(guò)數(shù)字濾波器的模擬。這種方法是在一個(gè)非常早期的DSP成功故事，講拼寫，廣泛銷售的兒童電子學(xué)習(xí)援助。</p><p>　　1.3.3 語(yǔ)

21、音識(shí)別</p><p>　　人類語(yǔ)音的自動(dòng)識(shí)別是非常多講話一代困難。語(yǔ)音識(shí)別是一個(gè)經(jīng)典的東西，人類的大腦好例子，但數(shù)碼電腦做的很差。數(shù)碼電腦可以存儲(chǔ)和調(diào)用大量數(shù)據(jù)，在熾烈速度執(zhí)行數(shù)學(xué)計(jì)算，并沒(méi)有變得無(wú)聊或低效重復(fù)的任務(wù)。不幸的是，現(xiàn)今電腦執(zhí)行得非常糟糕時(shí)，面臨著與原始的感官數(shù)據(jù)。教學(xué)計(jì)算機(jī)發(fā)送給您每月的電費(fèi)是很容易的。在同一臺(tái)計(jì)算機(jī)教學(xué)，以了解你的聲音，是一大創(chuàng)舉。</p><p>　　數(shù)

22、字信號(hào)處理一般接近語(yǔ)音識(shí)別的問(wèn)題，在兩個(gè)步驟：特征提取，特征匹配。傳入的??音頻信號(hào)中的每個(gè)單詞是孤立的，然后分析激發(fā)和共鳴頻率識(shí)別的類型。這些參數(shù)與前面的例子中，找出最接近的說(shuō)話。通常情況下，這些系統(tǒng)只有幾百字的限制，只能接受具有鮮明的字與字之間的停頓的講話，以及必須為各揚(yáng)聲器培訓(xùn)。雖然這是許多商業(yè)應(yīng)用提供足夠的，這些限制是震撼人心相比，人類的聽(tīng)覺(jué)能力。有巨大的財(cái)政獎(jiǎng)勵(lì)那些生產(chǎn)成功的商業(yè)產(chǎn)品，要在這方面做的大量工作。</p>

23、;<p><b>　　1.4 回聲定位</b></p><p>　　一個(gè)常用的方法是獲得遠(yuǎn)程對(duì)象的信息，超生波的關(guān)閉。例如，雷達(dá)通過(guò)發(fā)射無(wú)線電波脈沖，并從飛機(jī)回聲檢查接收到的信號(hào)。聲納，通過(guò)水傳播的聲波探測(cè)潛艇和其他水下物體。地球物理學(xué)家已經(jīng)長(zhǎng)探測(cè)地球所設(shè)置的爆炸和聽(tīng)回聲從巖石層深埋。雖然這些應(yīng)用都有一個(gè)共同的線程，每個(gè)人都有自己的具體問(wèn)題和需求。數(shù)字信號(hào)處理，在所有這三個(gè)領(lǐng)域

24、產(chǎn)生革命性的變化。</p><p><b>　　1.4.1 雷達(dá)</b></p><p>　　雷達(dá)是無(wú)線電探測(cè)和測(cè)距的縮寫。在最簡(jiǎn)單的雷達(dá)系統(tǒng)，無(wú)線電發(fā)射機(jī)產(chǎn)生的無(wú)線電頻率能量的脈沖長(zhǎng)幾微秒。此脈沖被送入一個(gè)高度定向天線，以光的速度在產(chǎn)生的無(wú)線電波傳播距離。飛機(jī)在這一波的路徑將反映能源回向接收天??線的一小部分，位于附近的傳輸站點(diǎn)。脈沖傳輸和接收到的回波之間的運(yùn)行時(shí)間

25、從計(jì)算到物體的距離。發(fā)現(xiàn)對(duì)象的方向更簡(jiǎn)單地說(shuō)，你知道你指出的定向天線時(shí)收到回音。</p><p>　　經(jīng)營(yíng)范圍的雷達(dá)系統(tǒng)是由兩個(gè)參數(shù)決定：多少能源是在初始脈沖，無(wú)線電接收機(jī)的噪聲水平。不幸的是，增加脈沖能量通常需要較長(zhǎng)的脈搏。反過(guò)來(lái)，在較長(zhǎng)的脈沖減少經(jīng)過(guò)時(shí)間的測(cè)量準(zhǔn)確度和精密度。這兩個(gè)重要參數(shù)之間的沖突結(jié)果：能夠在遠(yuǎn)距離探測(cè)的對(duì)象，并能準(zhǔn)確地判斷一個(gè)對(duì)象的距離。</p><p>　　DSP

26、具有革命性的雷達(dá)三個(gè)方面，所有這些都涉及到這個(gè)基本問(wèn)題。首先，DSP可以壓縮后收到的脈沖，提供更好的距離決心，沒(méi)有減少的經(jīng)營(yíng)范圍。其次，DSP可以過(guò)濾接收到的信號(hào)，以減少噪音。這擴(kuò)大了范圍，不降解的距離的決心。第三，DSP能夠快速選擇不同的脈沖形狀和長(zhǎng)度和發(fā)電。除其他事項(xiàng)外，這使得脈沖為一個(gè)特定的檢測(cè)問(wèn)題進(jìn)行了優(yōu)化?，F(xiàn)在這么多令人印象深刻的部分：是在采樣率可比使用的無(wú)線電頻率，高達(dá)幾百兆赫的！當(dāng)談到雷達(dá)，DSP硬件設(shè)計(jì)高速，因?yàn)樗撬惴?/p>

27、。</p><p><b>　　1.4.2 聲納</b></p><p>　　聲納是一個(gè)聲音導(dǎo)航和測(cè)距的縮寫。它分為兩大類，主動(dòng)和被動(dòng)。在主動(dòng)聲納，聲脈沖在2 kHz和40 kHz之間傳送入水，和由此產(chǎn)生的回聲的檢測(cè)和分析。主動(dòng)聲納的用途包括：海底機(jī)構(gòu)的檢測(cè)與定位，導(dǎo)航，通信，測(cè)繪海底。 10至100公里的一個(gè)最大的經(jīng)營(yíng)范圍是典型的。相比之下，被動(dòng)聲納根本監(jiān)聽(tīng)水下聲音

28、，其中包括：自然動(dòng)蕩，海洋生物，從潛艇和水面艦艇的機(jī)械聲音。由于被動(dòng)聲納發(fā)出能量，它是秘密行動(dòng)的理想選擇。你要檢測(cè)的其他人，沒(méi)有他偵測(cè)你。被動(dòng)聲納最重要的應(yīng)用是在軍事監(jiān)視系統(tǒng)，探測(cè)和跟蹤潛艇。被動(dòng)聲納通常使用較低的頻率比主動(dòng)聲納，因?yàn)樗麄兺ㄟ^(guò)吸收少水傳播。檢測(cè)范圍可以是數(shù)千公里。</p><p>　　DSP已徹底改變了許多在同一地區(qū)的雷達(dá)聲納：脈沖發(fā)生器，脈沖壓縮，過(guò)濾檢測(cè)到的信號(hào)。有一種觀點(diǎn)認(rèn)為，聲納比雷達(dá)簡(jiǎn)單

29、，因?yàn)樯婕邦l率較低。另一種觀點(diǎn)認(rèn)為，聲納是比雷達(dá)更困難，因?yàn)榄h(huán)境是少得多的統(tǒng)一和穩(wěn)定。聲納系統(tǒng)通常采用的發(fā)送和接收的元素，而不僅僅是一個(gè)單一渠道廣泛的陣列。通過(guò)適當(dāng)控制和混合信號(hào)，在這些眾多的元素，可以避開(kāi)聲納系統(tǒng)發(fā)射脈沖到所需的位置，并確定回聲收到的方向。為了處理這些多渠道，聲納系統(tǒng)需要作為雷達(dá)的同樣龐大的運(yùn)算能力。</p><p>　　1.4.3 反射地震</p><p>　　早在20

30、世紀(jì)20年代，地球物理學(xué)家發(fā)現(xiàn)，聲音探測(cè)地殼結(jié)構(gòu)可以?？碧秸呖赡芟破鸨ê陀涗涍吔鐚映^(guò)地表以下10公里的回聲。這些回聲地震解釋由原始的眼睛映射地下結(jié)構(gòu)。地震反射法迅速成為主要方法，為尋找石油和礦藏，今天依然如此。</p><p>　　在理想的情況下，到地面發(fā)出的聲音脈沖產(chǎn)生一個(gè)單脈沖穿過(guò)每個(gè)邊界層的回波。不幸的是，情況通常不是這么簡(jiǎn)單。每個(gè)回波返回到表面，必須通過(guò)所有其他邊界層以上，它起源。這可能會(huì)導(dǎo)致在層與層

31、之間的彈跳回聲，從而導(dǎo)致在表面上被檢測(cè)的回聲的回聲。這些二次相呼應(yīng)，可以檢測(cè)到的信號(hào)非常復(fù)雜和難以解釋的。數(shù)字信號(hào)處理技術(shù)已廣泛應(yīng)用于自1960年以來(lái)，隔離從二次回波反射地震主。早期地球物理學(xué)家怎么沒(méi)有D??SP管理？答案很簡(jiǎn)單：他們期待在方便的地方，多次反射最小化。 DSP的允許，在困難的地方，如大海，發(fā)現(xiàn)油。</p><p><b>　　1.5 影像處理</b></p>&

32、lt;p>　　圖像信號(hào)特色。首先，他們是一個(gè)空間（距離）超過(guò)參數(shù)的措施，而大多數(shù)信號(hào)是隨著時(shí)間的推移參數(shù)的措施。第二，它們包含了大量的信息。例如，超過(guò)10兆字節(jié)，可存儲(chǔ)一秒鐘的電視錄像。這是一千倍以上，比類似長(zhǎng)度的語(yǔ)音信號(hào)。第三，質(zhì)量的最終判斷往往是人類的主觀評(píng)價(jià)，而不是一個(gè)客觀的標(biāo)準(zhǔn)。這些特色使圖像處理DSP內(nèi)部的不同分組。</p><p><b>　　1.5.1 醫(yī)療</b><

33、;/p><p>　　在1895年，威廉·康拉德倫琴發(fā)現(xiàn)X射線可以通過(guò)大量的問(wèn)題。醫(yī)學(xué)革新的能力，看里面的活生生的人體。醫(yī)用X射線系統(tǒng)在僅僅幾年在世界各地傳播。盡管有其明顯的成功，醫(yī)用X射線成像由四個(gè)方面的問(wèn)題是有限的，直到DSP及相關(guān)技術(shù)在20世紀(jì)70年代。首先，在體內(nèi)的重疊結(jié)構(gòu)可以躲在彼此。例如，心臟部分可能不可見(jiàn)背后的肋骨。其次，它并不總是能夠區(qū)分類似的組織。例如，它可能是能夠從軟組織中分離出來(lái)的骨頭，

34、但不能區(qū)分肝腫瘤。第三，X射線圖像表明，人體的解剖結(jié)構(gòu)，而不是生理，身體的運(yùn)作。長(zhǎng)相酷似一個(gè)死一個(gè)的X射線圖像的X射線圖像，一個(gè)活生生的人！四，X射線照射可引起癌癥，要求它被只用謹(jǐn)慎和適當(dāng)?shù)睦碛伞?lt;/p><p>　　在1971年引進(jìn)的第一個(gè)電腦斷層掃描儀（以前稱為計(jì)算機(jī)軸向斷層掃描，或CAT掃描儀）的重疊結(jié)構(gòu)的問(wèn)題得到解決。計(jì)算機(jī)斷層掃描（CT）是數(shù)字信號(hào)處理的一個(gè)典型的例子。病人的身體正在審議的部分，通過(guò)X射

35、線從多個(gè)方向。 ，而不是簡(jiǎn)單的形成與檢測(cè)到的X射線圖像信號(hào)轉(zhuǎn)換成數(shù)字?jǐn)?shù)據(jù)，并存儲(chǔ)在計(jì)算機(jī)中。然后使用這些信息來(lái)計(jì)算，似乎是通過(guò)人體切片圖像。這些圖像表明遠(yuǎn)遠(yuǎn)大于傳統(tǒng)的技術(shù)細(xì)節(jié)，從而顯著提高診斷和治療。在CT的影響是幾乎一樣大的X射線成像本身的原始介紹。短短幾年，在世界的每一個(gè)大醫(yī)院有一個(gè)CT掃描儀的訪問(wèn)。 1979年，兩個(gè)CT的原則貢獻(xiàn)者，戈弗雷北路亨斯菲爾德和艾倫研究科馬克，分享諾貝爾醫(yī)學(xué)獎(jiǎng)。這是DSP的好！</p>&

36、lt;p>　　過(guò)去三年X射線的問(wèn)題已經(jīng)解決了用比其他X射線，如無(wú)線電和聲波穿透能量。 DSP在所有這些技術(shù)中起著關(guān)鍵作用。例如，磁共振成像（MRI）利用磁場(chǎng)與無(wú)線電波探測(cè)人體內(nèi)部。適當(dāng)調(diào)整的強(qiáng)度和頻率等領(lǐng)域引起原子核中的量子能態(tài)之間的身體產(chǎn)生共鳴的局部地區(qū)。在發(fā)射天線放在身體附近發(fā)現(xiàn)一所中學(xué)的無(wú)線電波，這種共振的結(jié)果。這個(gè)檢測(cè)信號(hào)的強(qiáng)度和其他特性提供關(guān)于在共振的局部地區(qū)的信息。磁場(chǎng)的調(diào)整，使整個(gè)身體的共振區(qū)域進(jìn)行掃描，映射的內(nèi)部結(jié)

37、構(gòu)。這種信息通常是圖像，就像在電腦斷層掃描。除了提供不同類型的軟組織之間的優(yōu)秀歧視，MRI可提供生理信息，如血流量，通過(guò)動(dòng)脈。磁共振完全依賴數(shù)字信號(hào)處理技術(shù)，并沒(méi)有他們不能實(shí)施。</p><p><b>　　1.5.2 空間</b></p><p>　　有時(shí)候，你只是做了一個(gè)不好的圖片最。這通常是從無(wú)人駕駛的衛(wèi)星和空間探測(cè)車拍攝的圖像的情況下。沒(méi)有人會(huì)派修理工到火星只

38、需要相機(jī)調(diào)整旋鈕！ DSP可以改善極為不利的條件，在幾個(gè)方面下拍攝的圖像質(zhì)量：亮度和對(duì)比度調(diào)整，邊緣檢測(cè)，降噪，重點(diǎn)調(diào)整，運(yùn)動(dòng)模糊減少，等有空間扭曲的圖像，如時(shí)遇到的是一個(gè)平面圖像一個(gè)球形的星球，也可以扭曲成一個(gè)正確的表示。許多單個(gè)圖像也可以被組合成一個(gè)單一的數(shù)據(jù)庫(kù)，允許以獨(dú)特的方式顯示信息。例如，在一個(gè)遙遠(yuǎn)的星球表面的空中飛行模擬視頻序列。</p><p>　　1.5.3 商業(yè)影像產(chǎn)品</p>&

39、lt;p>　　在圖像信息的內(nèi)容質(zhì)量數(shù)量向公眾出售的系統(tǒng)是一個(gè)問(wèn)題。商業(yè)系統(tǒng)必須是廉價(jià)的，這并不網(wǎng)格與大容量的存??儲(chǔ)器和高數(shù)據(jù)傳輸速率。這一困境的一個(gè)答案是圖像壓縮。正如語(yǔ)音信號(hào)，圖像包含大量的冗余信息，并可以通過(guò)算法，減少了代表他們所需要的數(shù)位運(yùn)行。電視和其他運(yùn)動(dòng)圖像壓縮尤其適合，因?yàn)榇蠖鄶?shù)的圖像仍然從幀到幀相同。商業(yè)影像產(chǎn)品，利用這種技術(shù)的優(yōu)點(diǎn)包括：視頻電話，計(jì)算機(jī)程序，顯示移動(dòng)的圖片和數(shù)字電視。</p><

40、;p>　　1 The Breadth and Depth of DSP</p><p>　　Digital Signal Processing is one of the most powerful technologies that will shape science and engineering in the twenty-first century. Revolutionary changes h

41、ave already been made in a broad range of fields: communications, medical imaging, radar & sonar, high fidelity music reproduction, and oil prospecting, to name just a few. Each of these areas has developed a deep DS

42、P technology, with its own algorithms, mathematics, and specialized techniques. This combination of breath and depth makes it</p><p>　　1.1 The Roots of DSP</p><p>　　Digital Signal Processing is

43、distinguished from other areas in computer science by the unique type of data it uses: signals. In most cases, these signals originate as sensory data from the real world: seismic vibrations, visual images, sound waves,

44、etc. DSP is the mathematics, the algorithms, and the techniques used to manipulate these signals after they have been converted into a digital form. This includes a wide variety of goals, such as: enhancement of visual i

45、mages, recognition and generati</p><p>　　The roots of DSP are in the 1960s and 1970s when digital computers first became available. Computers were expensive during this era, and DSP was limited to only a few

46、 critical applications. Pioneering efforts were made in four key areas: radar & sonar, where national security was at risk; oil exploration, where large amounts of money could be made; space exploration, where the da

47、ta are irreplaceable; and medical imaging, where lives could be saved. The personal computer revolution of the 1980s a</p><p>　　This technological revolution occurred from the top-down. In the early 1980s, D

48、SP was taught as a graduate level course in electrical engineering. A decade later, DSP had become a standard part of the undergraduate curriculum. Today, DSP is a basic skill needed by scientists and engineers in many f

49、ields. As an analogy, DSP can be compared to a previous technological revolution: electronics. While still the realm of electrical engineering, nearly every scientist and engineer has some background i</p><p&g

50、t;　　This recent history is more than a curiosity; it has a tremendous impact on your ability to learn and use DSP. Suppose you encounter a DSP problem, and turn to textbooks or other publications to find a solution. What

51、 you will typically find is page after page of equations, obscure mathematical symbols, and unfamiliar terminology. It's a nightmare! Much of the DSP literature is baffling even to those experienced in the field. It&

52、#39;s not that there is anything wrong with this material, it is just in</p><p>　　A basic premise of this book is that most practical DSP techniques can be learned and used without the traditional barriers o

53、f detailed mathematics and theory. The Scientist and Engineer’s Guide to Digital Signal Processing is written for those who want to use DSP as a tool, not a new career. </p><p>　　The remainder of this chapte

54、r illustrates areas where DSP has produced revolutionary changes. As you go through each application, notice that DSP is very interdisciplinary, relying on the technical work in many adjacent fields. As Fig. 1-2 suggests

55、, the borders between DSP and other technical disciplines are not sharp and well defined, but rather fuzzy and overlapping. If you want to specialize in DSP, these are the allied areas you will also need to study.</p&

56、gt;<p>　　1.2 Telecommunications</p><p>　　Telecommunications is about transferring information from one location to another. This includes many forms of information: telephone conversations, television

57、 signals, computer files, and other types of data. To transfer the information, you need a channel between the two locations. This may be a wire pair, radio signal, optical fiber, etc. Telecommunications companies receiv

58、e payment for transferring their customer's information, while they must pay to establish and maintain the channel. The f</p><p>　　1.2.1 Multiplexing</p><p>　　There are approximately one bil

59、lion telephones in the world. At the press of a few buttons, switching networks allow any one of these to be connected to any other in only a few seconds. The immensity of this task is mind boggling! Until the 1960s, a c

60、onnection between two telephones required passing the analog voice signals through mechanical switches and amplifiers. One connection required one pair of wires. In comparison, DSP converts audio signals into a stream of

61、 serial digital data. Since b</p><p>　　1.2.2 Compression</p><p>　　When a voice signal is digitized at 8000 samples/sec, most of the digital information is redundant. That is, the information car

62、ried by any one sample is largely duplicated by the neighboring samples. Dozens of DSP algorithms have been developed to convert digitized voice signals into data streams that require fewer bits/sec. These are called dat

63、a compression algorithms. Matching un-compression algorithms are used to restore the signal to its original form. These algorithms vary in the amount of</p><p>　　1.2.3 Echo control</p><p>　　Echo

64、es are a serious problem in long distance telephone connections. When you speak into a telephone, a signal representing your voice travels to the connecting receiver, where a portion of it returns as an echo. If the conn

65、ection is within a few hundred miles, the elapsed time for receiving the echo is only a few milliseconds. The human ear is accustomed to hearing echoes with these small time delays, and the connection sounds quite normal

66、. As the distance becomes larger, the echo becomes incre</p><p>　　1.3 Audio Processing</p><p>　　The two principal human senses are vision and hearing. Correspondingly, much of DSP is related to

67、image and audio processing. People listen to both music and speech. DSP has made revolutionary changes in both these areas.</p><p>　　1.3.1 Music</p><p>　　The path leading from the musician's

68、 microphone to the audiophile's speaker is remarkably long. Digital data representation is important to prevent the degradation commonly associated with analog storage and manipulation. This is very familiar to anyon

69、e who has compared the musical quality of cassette tapes with compact disks. In a typical scenario, a musical piece is recorded in a sound studio on multiple channels or tracks. In some cases, this even involves recordin

70、g individual instruments and</p><p>　　One of the most interesting DSP applications in music preparation is artificial reverberation. If the individual channels are simply added together, the resulting piece

71、sounds frail and diluted, much as if the musicians were playing outdoors. This is because listeners are greatly influenced by the echo or reverberation content of the music, which is usually minimized in the sound studio

72、. DSP allows artificial echoes and reverberation to be added during mix down to simulate various ideal listenin</p><p>　　1.3.2 Speech generation</p><p>　　Speech generation and recognition are us

73、ed to communicate between humans and machines. Rather than using your hands and eyes, you use your mouth and ears. This is very convenient when your hands and eyes should be doing something else, such as: driving a car,

74、performing surgery, or (unfortunately) firing your weapons at the enemy. Two approaches are used for computer generated speech: digital recording and vocal tract simulation. In digital recording, the voice of a human spe

75、aker is digitized an</p><p>　　Vocal tract simulators are more complicated, trying to mimic the physical mechanisms by which humans create speech. The human vocal tract is an acoustic cavity with resonant fre

76、quencies determined by the size and shape of the chambers. Sound originates in the vocal tract in one of two basic ways, called voiced and fricative sounds. With voiced sounds, vocal cord vibration produces near periodic

77、 pulses of air into the vocal cavities. In comparison, fricative sounds originate from the noisy air tu</p><p>　　1.3.3 Speech recognition</p><p>　　The automated recognition of human speech is im

78、mensely more difficult than speech generation. Speech recognition is a classic example of things that the human brain does well, but digital computers do poorly. Digital computers can store and recall vast amounts of dat

79、a, perform mathematical calculations at blazing speeds, and do repetitive tasks without becoming bored or inefficient. Unfortunately, present day computers perform very poorly when faced with raw sensory data. Teaching a

80、 computer to </p><p>　　Digital Signal Processing generally approaches the problem of voice recognition in two steps: feature extraction followed by feature matching. Each word in the incoming audio signal is

81、 isolated and then analyzed to identify the type of excitation and resonate frequencies. These parameters are then compared with previous examples of spoken words to identify the closest match. Often, these systems are l

82、imited to only a few hundred words; can only accept speech with distinct pauses between words; a</p><p>　　1.4 Echo Location</p><p>　　A common method of obtaining information about a remote objec

83、t is to bounce a wave off of it. For example, radar operates by transmitting pulses of radio waves, and examining the received signal for echoes from aircraft. In sonar, sound waves are transmitted through the water to d

84、etect submarines and other submerged objects. Geophysicists have long probed the earth by setting off explosions and listening for the echoes from deeply buried layers of rock. While these applications have a common thr&

85、lt;/p><p>　　1.4.1 Radar</p><p>　　Radar is an acronym for Radio Detection And Ranging. In the simplest radar system, a radio transmitter produces a pulse of radio frequency energy a few microseconds

86、 long. This pulse is fed into a highly directional antenna, where the resulting radio wave propagates away at the speed of light. Aircraft in the path of this wave will reflect a small portion of the energy back toward a

87、 receiving antenna, situated near the transmission site. The distance to the object is calculated from the elapsed t</p><p>　　The operating range of a radar system is determined by two parameters: how much e

88、nergy is in the initial pulse, and the noise level of the radio receiver. Unfortunately, increasing the energy in the pulse usually requires making the pulse longer. In turn, the longer pulse reduces the accuracy and pre

89、cision of the elapsed time measurement. This results in a conflict between two important parameters: the ability to detect objects at long range, and the ability to accurately determine an object's d</p><p

90、>　　DSP has revolutionized radar in three areas, all of which relate to this basic problem. First, DSP can compress the pulse after it is received, providing better distance determination without reducing the operating

91、 range. Second, DSP can filter the received signal to decrease the noise. This increases the range, without degrading the distance determination. Third, DSP enables the rapid selection and generation of different pulse s

92、hapes and lengths. Among other things, this allows the pulse to be</p><p>　　1.4.2 Sonar</p><p>　　Sonar is an acronym for Sound Navigation and Ranging. It is divided into two categories, active a

93、nd passive. In active sonar, sound pulses between 2 kHz and 40 kHz are transmitted into the water, and the resulting echoes detected and analyzed. Uses of active sonar include: detection & localization of undersea bo

94、dies, navigation, communication, and mapping the sea floor. A maximum operating range of 10 to 100 kilometers is typical. In comparison, passive sonar simply listens to underwater sounds,</p><p>　　DSP has re

95、volutionized sonar in many of the same areas as radar: pulse generation, pulse compression, and filtering of detected signals. In one view, sonar is simpler than radar because of the lower frequencies involved. In anothe

96、r view, sonar is more difficult than radar because the environment is much less uniform and stable. Sonar systems usually employ extensive arrays of transmitting and receiving elements, rather than just a single channel.

97、 By properly controlling and mixing the signals in</p><p>　　1.4.3 Reflection seismology</p><p>　　As early as the 1920s, geophysicists discovered that the structure of the earth's crust could

98、 be probed with sound. Prospectors could set off an explosion and record the echoes from boundary layers more than ten kilometers below the surface. These echo seismograms were interpreted by the raw eye to map the subsu

99、rface structure. The reflection seismic method rapidly became the primary method for locating petroleum and mineral deposits, and remains so today.</p><p>　　In the ideal case, a sound pulse sent into the gro

100、und produces a single echo for each boundary layer the pulse passes through. Unfortunately, the situation is not usually this simple. Each echo returning to the surface must pass through all the other boundary layers abo

101、ve where it originated. This can result in the echo bouncing between layers, giving rise to echoes of echoes being detected at the surface. These secondary echoes can make the detected signal very complicated and difficu