【正文】 traction, signal editing, etc. One of the most interesting DSP applications in music preparation is artificial reverberation. If the individual channels are simply added together, the resulting piece 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. DSP allows artificial echoes and reverberation to be added during mix down to simulate various ideal listening environments. Echoes with delays of a few hundred milliseconds give the impression of cathedral like locations. Adding echoes with delays of 1020 milliseconds provide the perception of more modest size listening rooms. Speech generation Speech generation and recognition are used to municate 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, performing surgery, or (unfortunately) firing your weapons at the enemy. Two approaches are used for puter generated speech: digital recording and vocal tract simulation. In digital recording, the voice of a human speaker is digitized and stored, usually in a pressed form. During playback, the stored data are unpressed and converted back into an analog signal. An entire hour of recorded speech requires only about three megabytes of storage, well within the capabilities of even small puter systems. This is the most mon method of digital speech generation used today. Vocal tract simulators are more plicated, trying to mimic the physical mechanisms by which humans create speech. The human vocal tract is an acoustic cavity with resonant frequencies 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 pulses of air into the vocal cavities. In parison, fricative sounds originate from the noisy air turbulence at narrow constrictions, such as the teeth and lips. Vocal tract simulators operate by generating digital signals that resemble these two types of excitation. The characteristics of the resonate chamber are simulated by passing the excitation signal through a digital filter with similar resonances. This approach was used in one of the very early DSP success stories, the Speak amp。s not that there is anything wrong with this material, it is just intended for a very specialized audience. Stateoftheart researchers need this kind of detailed mathematics to understand the theoretical implications of the work. 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. 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. The remainder of this chapter 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. 12 suggests, 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. Telemunications Telemunications is about transferring information from one location to another. This includes many forms of information: telephone conversations, television signals, puter 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. Telemunications panies receive payment for transferring their customer39。 space exploration, where the data are irreplaceable。 1 The Breadth and Depth of DSP Digital Signal Processing is one of the most powerful technologies that will shape science and engineering in the twentyfirst century. Revolutionary changes have already been made in a broad range of fields: munications, medical imaging, radar amp。這一困境的一個答案是圖像壓縮。許多單個圖像也可以被組合成一個單一的數(shù)據(jù)庫，允許以獨特的方式顯示信息。磁共振完全依賴數(shù)字信號處 理技術(shù)，并沒有他們不能實施。這個檢測信號的強度和其他特性提供關(guān)于在共振的局部地區(qū)的信息。 DSP 在所有這些技術(shù)中起著關(guān)鍵作用。在 CT 的影響是幾乎一樣大的 X射線成像本身的原始介紹。病人的身體正在審議的部分，通過 X 射線從多個方向。第三， X 射線圖像表明，人體的解剖結(jié)構(gòu)，而不是生理，身體的運作。首先，在體內(nèi)的重疊結(jié)構(gòu)可以躲在彼此?？道聜惽侔l(fā)現(xiàn) X 射線可以通過大量的問題。這是一千倍以上，比類似長度的語音信號。 影像處理 圖像信號特色。這些二次相呼應(yīng)，可以檢測到的信號非常復(fù)雜和難以解釋的。 在理想的情況下，到地面發(fā)出的聲音脈沖產(chǎn)生一個單脈沖穿過每個邊 界層的回波。 反射地震 早在 20 世紀 20 年代，地球物理學(xué)家發(fā)現(xiàn)，聲音探測地殼結(jié)構(gòu)可以。另一種觀點認為，聲納是比雷達更困難，因為環(huán)境是少得多的統(tǒng)一和穩(wěn)定。被動聲納通常使用較低的頻率比主動聲納，因為他們通過吸收少水傳播。相比之下，被動聲納根本監(jiān)聽水下聲音 ，其中包括：自然動蕩，海洋生物，從潛艇和水面艦艇的機械聲音。它分為兩大類，主動和被動。第三， DSP 能夠快速選擇不同的脈 沖形狀和長度和發(fā)電。 DSP 具有革命性的雷達三個方面，所有這些都涉及到這個基本問題。 經(jīng)營范圍的雷達系統(tǒng)是由兩個參數(shù)決定：多少能源是在初始脈沖，無線電接收機的噪聲水平。此脈沖被送入一個高度定向天線，以光的速度在產(chǎn)生的無線電波傳播距離。雖然這些應(yīng)用都有一個共同的線程，每個人都有自己的具體問題和需求。 回聲定位 一個常用的方法是獲得遠程對象的信息，超生波的關(guān)閉。這些參數(shù)與前面的例子中，找出最接近的說話。教學(xué)計算機發(fā)送給您每月的電費是很容易的。 語音識別 人類語音的自動識別是非常多講話一代困難。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。 聲道模擬器比較復(fù)雜，試圖模仿人類創(chuàng)造講話的物理機制。在數(shù)碼錄音，一個人的揚聲器的聲音數(shù)字化處理和儲存，通常在壓縮形式。 語音生成 語音生成和識別被用于人類和機器之間的溝通。這是因為聽眾都深受影響的音樂，通常是在錄音室最小的回聲或混響內(nèi)容。被稱為復(fù)雜的過程，結(jié)合到最終產(chǎn)品的個別曲目的縮混。這是非常熟悉的人與光盤，錄音帶的音樂素質(zhì)。人們聽音樂和語音。同樣的技術(shù)，允許免提電話用戶聽取和不戰(zhàn)而音頻反饋（嘯）在同一時間發(fā)言。人類的耳朵習(xí)慣于聽到這些小的時間延遲的回聲，連接聽起來很正常。達到的最高壓縮約 2 千比特 /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。匹配解壓縮算法，用于恢復(fù)其原來的形式的信號。 壓縮 當語音信號數(shù)字化，在 8000 樣本 /秒，大多數(shù)的數(shù)字信息是多余的。這個結(jié)果在 64,000 比特 /秒，所有 24 個被包含在 兆比特 /秒的渠道代表每個語音信號。相比之下， DSP 音頻信號轉(zhuǎn)換成串行數(shù)字數(shù)據(jù)流。 復(fù)用 在世界上大約有 10 億電話。傳輸信息，你需要在兩個地點之間的通道。正如圖。 這本書的一個基本前提是，可以學(xué)到最實用的 DSP 技術(shù)，并沒有詳細的數(shù)學(xué)和理論的傳統(tǒng)障礙。你通常會發(fā)現(xiàn)什么是頁后頁方程，模糊的數(shù)學(xué)符號，不熟悉的術(shù)語。沒有它，他們將失去在科技世界。十年后， DSP 已成為標準的本科課程的一部分。任何人士如認為他們可以使資金在迅速擴大的領(lǐng)域突然一個 DSP 供應(yīng)商。太空探索，其中的數(shù)據(jù) 是不可替代的 。這包括了各種目標，如：加強視覺圖像識別和語音生成，存儲和傳輸?shù)臄?shù)據(jù)壓縮，等假設(shè)我們重視計算機模擬 數(shù)字轉(zhuǎn)換器，并用它來獲得一個現(xiàn)實世界的