專業(yè)外語-多媒體-音頻信號

1、Lecture 15: Introduction to multimedia: audio2013.5Outline Background Text tour Vocabulary Difficult points Text tour 英譯漢 漢譯英背景介紹(Background) 在計算機系統(tǒng)中，組合兩種或兩種以上媒體的一種人機交互式信息交流和傳播媒體。使用的媒體包括文字、圖片、聲音 (包含音樂、語音旁白、特殊音效)、動畫和影片，以及程式所提供的互動功能。 本講中重點講解多媒體中的音頻與圖像方面的知識 音頻部分包括音頻傳輸、音頻壓縮、音頻格式等內(nèi)容。 圖像部分包括圖像基本知識、圖像壓縮、圖像

2、格式等。語音頻率與采樣 人耳聽到的語音頻率范圍為20Hz-20kHz。其中，人耳對1kHz-4kHz范圍的語音頻率最為敏感。 根據(jù)尼奎斯特采樣定理，要獲得不失真的語音信號，采樣頻率需在40kHz以上。例如，高保真音頻采用44.1kHz采樣頻率。 為了傳輸需要，很多系統(tǒng)(如電話系統(tǒng))采用8kHz采樣頻率，保留語音中對人類最敏感的頻率部分。 語音合成技術(shù)（如線性預測編碼:LPC）可以更大限度的壓縮語音信號。音頻制式：MP3 MPEG: Moving Picture Experts Group (動態(tài)圖像專家組)。MPEG標準主要有以下五個，MPEG-1、MPEG-2、MPEG-4、MPEG-7及M

3、PEG-21等。該專家組建于1988年，專門負責為CD建立視頻和音頻標準 MP3：MPEG-1 audio layer 3Paragraph 1Multimedia is media and content that uses a combination of different content forms. Multimedia includes a combination of text, audio, still images, animation, video, or interactivity content forms. Multimedia is usually recorded

4、 and played, displayed, or accessed by information content processing devices, such as computerized and electronic devices, but can also be part of a live performance. Multimedia devices are electronic media devices used to store and experience multimedia content. Multimedia is distinguished from mi

5、xed media in fine art; by including audio, for example, it has a broader scope. The term “rich media” is synonymous for interactive multimedia. Hypermedia can be considered one particular multimedia application. From WikipediaVocabulary Multimedia: 多媒體 Content forms: 內(nèi)容格式 Animation: 動畫 Interactivity

6、：相互，交互 Store：存儲 Mixed media：復合媒體，綜合材料 Device: 器件，設(shè)備Vocabulary Still image: 靜態(tài)圖像 Video：視頻 Audio: 音頻 Text：文字 Hypermedia： 超媒體 Synonymous： 代名詞 Rich media: 富媒體，互動式媒體 Live performance: 現(xiàn)場表演Difficult pointMultimedia includes a combination of text, audio, still images, animation, video, or interactivity con

7、tent forms. a combination of: 組合 翻譯：多媒體是由文字、音頻、靜態(tài)圖像、動畫、視頻及交互程序組合而成的。Difficult point Multimedia is usually recorded and played, displayed, or accessed by information content processing devices, such as computerized and electronic devices access: 存取，訪問。 例如：程序設(shè)計中，指針的非法訪問會報錯access violation。 翻譯：多媒體一般是利用

8、信息處理設(shè)備如電子與計算機設(shè)備來對媒體內(nèi)容進行記錄和播放、顯示與存取。Difficult point Multimedia is distinguished from mixed media in fine art; distinguish from: 與。區(qū)別翻譯：多媒體與美術(shù)中的復合媒體是不一樣的。Paragraph 2 CD-quality audio requires a transmission bandwidth of 1.411 Mbps. Clearly, substantial compression is needed to make transmission over t

9、he Internet practical. For this reason, various audio compression algorithms have been developed. Probably the most popular one is MPEG audio, which has three layers (variants), of which MP3 (MPEG audio layer 3) is the most powerful and best known. Large amounts of music in MP3 format are available

10、on the Internet, not all of it legal, which has resulted in numerous lawsuits from the artists and copyright owners. MP3 belongs to the audio portion of the MPEG video compression standard. Vocabulary CD-quality: CD音質(zhì) Transmission bandwidth: 傳輸帶寬 Compression: 壓縮 substantial compression：高度壓縮 MPEG：Mov

11、ing Pictures Experts Group，多媒體一種常用格式 MP3：MPEG-1 Audio Layer 3Vocabulary Algorithms： 算法 Legal: 合法的 Lawsuit：訴訟 Portion: 組成部分 Numerous：大量的 Available: 可用的 Copyright：版權(quán) Standard：標準Difficult point CD-quality audio requires a transmission bandwidth of 1.411 Mbps. CD-quality audio: 高音質(zhì)音頻 翻譯：傳送高音質(zhì)音頻需要1.411兆帶

12、寬。 Difficult point Large amounts of music in MP3 format are available on the Internet, not all of it legal, which has resulted in numerous lawsuits from the artists and copyright owners. result in: 導致，由此而來 翻譯：互聯(lián)網(wǎng)上有大量的MP3格式的音樂資源。但是，由于版權(quán)問題，它們有些是非法的。藝術(shù)創(chuàng)作者與版權(quán)所有者提起的大量訴訟案件也由此而來。Paragraph 3 Table 1 shows t

13、he tradeoff between sound quality and data rate for these three categories. High fidelity music system sample fast enough (44.1 kHz), and with enough precision (16 bits), that they can capture virtually all of the sounds that humans are capable of hearing. This magnificent sound quality comes at the

14、 price of a high data rate, 44.1kHz16bits= 706kbits/sec. This is pure brute force. Vocabulary Tradeoff: 平衡的，折中的 High fidelity music:高保真音樂 Precision: 精度 Virtually： 簡直，實質(zhì)上 Magnificent: 華麗的，優(yōu)秀的 Capture：采集，捕捉 Difficult point Table 1 shows the tradeoff between sound quality and data rate for these three

15、categories. Tradeoff between: 兼顧，折中考慮，平衡 翻譯：表1顯示這三種音頻制式對音質(zhì)與數(shù)據(jù)碼率這兩個指標上折中考慮。Difficult point This magnificent sound quality comes at the price of a high data rate, 44.1kHz16bits= 706kbits/sec. at the price of: 付出.的代價 翻譯：高音質(zhì)帶來的代價就是高達706kbits/sec的數(shù)據(jù)碼率。英譯漢 The range of human hearing is generally considere

16、d to be 20 Hz to 20 kHz, but it is far more sensitive to sounds between 1 kHz and 4 kHz. For example, listeners can detect sounds as low as 0 dB SPL at 3 kHz, but require 40 dB SPL at 100 hertz (an amplitude increase of 100). Listeners can tell that two tones are different if their frequencies diffe

17、r by more than about 0.3% at 3 kHz. This increases to 3% at 100 hertz. For comparison, adjacent keys on a piano differ by about 6% in frequency. 英譯漢 Audio processing covers many diverse fields, all involved in presenting sound to human listeners. Three areas are prominent: (1) high fidelity music reproduction, such as in audio compact discs, (2) voice telecommunications, another name for telephone networks, and (3) synthetic speech, where computers generate and recognize human voice patterns. While these applications have different goals and problems, they are link