专业外语-多媒体-音频信号

Lecture15:Introductiontomultimedia:audio2013.5OutlineBackgroundTexttourVocabularyDifficultpointsTexttour英译汉汉译英背景介绍(Background)在计算机系统中，组合两种或两种以上媒体的一种人机交互式信息交流和传播媒体。使用的媒体包括文字、图片、声音(包含音乐、语音旁白、特殊音效)、动画和影片，以及程式所提供的互动功能。本讲中重点讲解多媒体中的音频与图像方面的知识音频部分包括音频传输、音频压缩、音频格式等内容。图像部分包括图像基本知识、图像压缩、图像格式等。语音频率与采样人耳听到的语音频率范围为20Hz-20kHz。其中，人耳对1kHz-4kHz范围的语音频率最为敏感。根据尼奎斯特采样定理，要获得不失真的语音信号，采样频率需在40kHz以上。例如，高保真音频采用44.1kHz采样频率。

为了传输需要，很多系统(如电话系统)采用8kHz采样频率，保留语音中对人类最敏感的频率部分。语音合成技术（如线性预测编码:LPC）可以更大限度的压缩语音信号。音频制式：MP3MPEG:MovingPictureExpertsGroup(动态图像专家组)。MPEG标准主要有以下五个，MPEG-1、MPEG-2、MPEG-4、MPEG-7及MPEG-21等。该专家组建于1988年，专门负责为CD建立视频和音频标准MP3：MPEG-1audiolayer3Paragraph1 Multimediaismediaandcontentthatusesacombinationofdifferentcontentforms.Multimediaincludesacombinationoftext,audio,stillimages,animation,video,orinteractivitycontentforms.Multimediaisusuallyrecordedandplayed,displayed,oraccessedbyinformationcontentprocessingdevices,suchascomputerizedandelectronicdevices,butcanalsobepartofaliveperformance.Multimediadevicesareelectronicmediadevicesusedtostoreandexperiencemultimediacontent.Multimediaisdistinguishedfrommixedmediainfineart;byincludingaudio,forexample,ithasabroaderscope.Theterm“richmedia”issynonymousforinteractivemultimedia.Hypermediacanbeconsideredoneparticularmultimediaapplication. FromWikipediaVocabularyMultimedia:多媒体Contentforms:内容格式Animation:动画Interactivity：相互，交互Store：存储Mixedmedia：复合媒体，综合材料Device:器件，设备VocabularyStillimage:静态图像Video：视频Audio:音频Text：文字Hypermedia：超媒体Synonymous：代名词Richmedia:富媒体，互动式媒体Liveperformance:现场表演DifficultpointMultimediaincludesacombinationoftext,audio,stillimages,animation,video,orinteractivitycontentforms.acombinationof:组合翻译：多媒体是由文字、音频、静态图像、动画、视频及交互程序组合而成的。DifficultpointMultimediaisusuallyrecordedandplayed,displayed,oraccessedbyinformationcontentprocessingdevices,suchascomputerizedandelectronicdevicesaccess:存取，访问。例如：程序设计中，指针的非法访问会报错"accessviolation"。翻译：多媒体一般是利用信息处理设备如电子与计算机设备来对媒体内容进行记录和播放、显示与存取。DifficultpointMultimediaisdistinguishedfrommixedmediainfineart;distinguishfrom:与。。。区别翻译：多媒体与美术中的复合媒体是不一样的。Paragraph2CD-qualityaudiorequiresatransmissionbandwidthof1.411Mbps.Clearly,substantialcompressionisneededtomaketransmissionovertheInternetpractical.Forthisreason,variousaudiocompressionalgorithmshavebeendeveloped.ProbablythemostpopularoneisMPEGaudio,whichhasthreelayers(variants),ofwhichMP3(MPEGaudiolayer3)isthemostpowerfulandbestknown.LargeamountsofmusicinMP3formatareavailableontheInternet,notallofitlegal,whichhasresultedinnumerouslawsuitsfromtheartistsandcopyrightowners.MP3belongstotheaudioportionoftheMPEGvideocompressionstandard.VocabularyCD-quality:CD音质Transmissionbandwidth:传输带宽Compression:压缩substantialcompression：高度压缩MPEG：MovingPicturesExpertsGroup，多媒体一种常用格式MP3：MPEG-1AudioLayer3VocabularyAlgorithms：算法Legal:合法的Lawsuit：诉讼Portion:组成部分Numerous：大量的Available:可用的Copyright：版权Standard：标准DifficultpointCD-qualityaudiorequiresatransmissionbandwidthof1.411Mbps.CD-qualityaudio:高音质音频翻译：传送高音质音频需要1.411兆带宽。

DifficultpointLargeamountsofmusicinMP3formatareavailableontheInternet,notallofitlegal,whichhasresultedinnumerouslawsuitsfromtheartistsandcopyrightowners.resultin:导致，由此而来翻译：互联网上有大量的MP3格式的音乐资源。但是，由于版权问题，它们有些是非法的。艺术创作者与版权所有者提起的大量诉讼案件也由此而来。Paragraph3Table1showsthetradeoffbetweensoundqualityanddatarateforthesethreecategories.Highfidelitymusicsystemsamplefastenough(44.1kHz),andwithenoughprecision(16bits),thattheycancapturevirtuallyallofthesoundsthathumansarecapableofhearing.Thismagnificentsoundqualitycomesatthepriceofahighdatarate,44.1kHz×16bits=706kbits/sec.Thisispurebruteforce.VocabularyTradeoff:平衡的，折中的Highfidelitymusic:高保真音乐Precision:精度Virtually：简直，实质上Magnificent:华丽的，优秀的Capture：采集，捕捉DifficultpointTable1showsthetradeoffbetweensoundqualityanddatarateforthesethreecategories.Tradeoffbetween:兼顾，折中考虑，平衡翻译：表1显示这三种音频制式对音质与数据码率这两个指标上折中考虑。DifficultpointThismagnificentsoundqualitycomesatthepriceofahighdatarate,44.1kHz×16bits=706kbits/sec.atthepriceof:付出...的代价翻译：高音质带来的代价就是高达706kbits/sec的数据码率。英译汉Therangeofhumanhearingisgenerallyconsideredtobe20Hzto20kHz,butitisfarmoresensitivetosoundsbetween1kHzand4kHz.Forexample,listenerscandetectsoundsaslowas0dBSPLat3kHz,butrequire40dBSPLat100hertz(anamplitudeincreaseof100).Listenerscantellthattwotonesaredifferentiftheirfrequenciesdifferbymorethanabout0.3%at3kHz.Thisincreasesto3%at100hertz.Forcomparison,adjacentkeysonapianodifferbyabout6%infrequency.英译汉Audioprocessingcoversmanydiversefields,allinvolvedinpresentingsoundtohumanlisteners.Threeareasareprominent:(1)highfidelitymusicreproduction,suchasinaudiocompactdiscs,(2)voicetelecommunications,anothernamefortelephonenetworks,and(3)syntheticspeech,wherecomputersgenerateandrecognizehumanvoicepatterns.Whiletheseapplicationshavedifferentgoalsandproblems,theyarelinkedbyacommonumpi