Lesson20MP3AudioCompression《電子信息工程專業英語教程（第5版）》Unit7Audio&SpeechLesson20AudioCompressionBackgroundsTexttour

LanguageinuseVocabularyStructureReading/writingtechniques2024/5/292《電子信息工程專業英語教程（第5版）》TerminologyCD-qualityaudio

CD音質音頻transmissionbandwidth

傳輸帶寬waveformcoding

波形編碼perceptualcoding

知覺編碼Backgrounds2024/5/293《電子信息工程專業英語教程（第5版）》Terminologyauditorysystem

聽覺系統frequencymasking

頻率屏蔽temporalmasking

暫時屏蔽constant-amplitude

固定幅度Backgrounds2024/5/294《電子信息工程專業英語教程（第5版）》Terminologyspectralresolution

頻譜分辨率SNR:signal-to-noiseratio

信噪比Backgrounds2024/5/295《電子信息工程專業英語教程（第5版）》TexttourOutlineIntroduction(para.1)FrequencyMaskingandPerceptualCoding (para.2-8)TheStepsofMP3Encoding(para.9-13)2024/5/296《電子信息工程專業英語教程（第5版）》IntroductionCD-qualityaudiorequiresatransmissionbandwidthof1.411Mbps.TomaketransmissionovertheInternetpractical,audiocompressionalgorithmsaredevelopedMP3(MPEGaudiolayer3)isthemostpowerfulandbestknown2024/5/297《電子信息工程專業英語教程（第5版）》FrequencyMaskingandPerceptualCodingAudiocompressioncanbedoneinoneoftwowayswaveformcodingperceptualcoding,MP3isbasedonperceptualcoding.2024/5/298《電子信息工程專業英語教程（第5版）》FrequencyMaskingandPerceptualCodingExampleExperiment1Experiment22024/5/299《電子信息工程專業英語教程（第5版）》FrequencyMaskingandPerceptualCoding(a)Thethresholdofaudibilityasafunctionoffrequency(b)Themaskingeffect2024/5/2910《電子信息工程專業英語教程（第5版）》TheStepsofMP3EncodingSamplingthewaveformat32kHz,44.1kHz,or48kHz.Samplingcanbedoneononeortwochannels,inanyoffourconfigurations:Monophonic(asingleinputstream).Dualmonophonic(e.g.,anEnglishandaJapanesesoundtrack).Disjointstereo(eachchannelcompressedseparately).Jointstereo(interchannelredundancyfullyexploited).2024/5/2911《電子信息工程專業英語教程（第5版）》TheStepsofMP3EncodingTheoutputbitrateischosen.Foraastereorock’nrollCD,downto96kbpswithlittleperceptiblelossinqualityForapianoconcert,atleast128kbpsareneeded.2024/5/2912《電子信息工程專業英語教程（第5版）》TheStepsofMP3EncodingThesamplesareprocessedingroupsof1152(about26msecworth).Eachgroupisfirstpassedthrough32digitalfilterstoget32frequencybands.Atthesametime,theinputisfedintoapsychoacousticmodelinordertodeterminethemaskedfrequencies.2024/5/2913《電子信息工程專業英語教程（第5版）》TheStepsofMP3EncodingNext,eachofthe32frequencybandsisfurthertransformedtoprovideafinerspectralresolution.Inthenextphase,theavailablebitbudgetisdividedamongthebandsmorebitsallocatedtothebandswiththemostunmaskedspectralpowerfewerbitsallocatedtounmaskedbandswithlessspectralpowernobitsallocatedtomaskedbands.Finally,thebitsareencodedusingHuffmanencoding

2024/5/2914《電子信息工程專業英語教程（第5版）》TheStepsofMP3EncodingThereisactuallymoretothestory.Varioustechniquesarealsousedfornoisereductionantialiasingexploitingtheinterchannelredundancy…2024/5/2915《電子信息工程專業英語教程（第5版）》VocabularyAllocateperceptibleresolutionTransmissionStructureReading/writingtechniquesLanguageinuse2024/5/2916《電子信息工程專業英語教程（第5版）》Vocabulary2024/5/2917《電子信息工程專業英語教程（第5版）》AllocateindictionaryTosetapartforaspecialpurpose;designate:

分配；指定allocatearoomtobeusedforstorage.Todistributeaccordingtoaplan;allot:

分撥；分配allocaterationsforaweek-longcampingtrip.2024/5/2918《電子信息工程專業英語教程（第5版）》AllocateindictionaryToassignaresource,suchasadiskoradiskettefile,toaspecifictask.

為指定的任務分配資源Toassignmainroutinesandsubroutinestostorage.

為程序分配存儲器2024/5/2919《電子信息工程專業英語教程（第5版）》AllocateintextInthenextphasetheavailablebitbudgetisdividedamongthebands,withmorebitsallocatedtothebandswiththemostunmaskedspectralpower,fewerbitsallocatedtounmaskedbandswithlessspectralpower,andnobitsallocatedtomaskedbands.Finally,thebitsareencodedusingHuffmanencoding,whichassignsshortcodestonumbersthatappearfrequentlyandlongcodestothosethatoccurinfrequently.下一步，將可用的位數分配給各個頻帶，擁有最多的未被屏蔽譜功率的頻帶分配較多的位數，擁有較少未被屏蔽譜功率的頻帶分配較少的位數，而完全屏蔽的頻帶不分配位數。最后，用哈夫曼編碼機制對這些數據位進行編碼。哈夫曼編碼將短碼字分配給出現頻繁的數據，而將長碼字分配給出現頻率不高的數據。2024/5/2920《電子信息工程專業英語教程（第5版）》Allocateinuse

allocateappropriatedesignateearmark

Thecentralmeaningsharedbytheseverbsistosetasideforaspecifiedpurpose

allocatedtimeforrecreationappropriatedfundsforpubliceducationdesignatedalocationforthenewhospitalmoneyearmarkedforavacation2024/5/2921《電子信息工程專業英語教程（第5版）》Allocateinuse

assignallotapportionallocate Theseverbsmeantosetasideorgiveoutinportionsorshares.

Bothassign,whichappliestoanauthoritativeact,andallotrefertoarbitrarydistribution,butneitherimpliesequalityorfairnessofdivision:

Thehardestworkwasassignedtothestrongestlaborers.Weallotahalfhouradayforrecreation.2024/5/2922《電子信息工程專業英語教程（第5版）》Allocateinuse

assignallotapportionallocate

Toapportionistodivideaccordingtoprescribedrulesandimpliesfairdistribution:ThefirstdutyofalegislatoristoapportionpenaltiesAllocateusuallymeanstosetsomethingapartfromalargerquantity,asofmoney,foraspecificpurposeorforaparticularpersonorgroupAportionofthebudgetwasallocatedfortheeducationofeachstudent.2024/5/2923《電子信息工程專業英語教程（第5版）》PerceptibleindictionaryCapableofbeingperceivedbythesensesorthemind:

可感知的perceptiblesoundsinthenight.2024/5/2924《電子信息工程專業英語教程（第5版）》PerceptibleintextFirst,theoutputbitrateischosen.MP3cancompressastereorock'nrollCDdownto96kbpswithlittleperceptible

lossinquality,evenforrock‘nrollfanswithnohearingloss.首先，要選擇輸出數據率。MP3能將一張搖滾樂CD壓縮至96Kbps，而幾乎沒有可覺察的音質下降；即便是搖滾樂愛好者也聽不出音質的下降。2024/5/2925《電子信息工程專業英語教程（第5版）》Perceptibleinuse

perceptiblepalpableappreciablenoticeablediscernible Theseadjectivesapplytowhatiscapableofbeingapprehendedwiththemindorthroughthesensesasbeingreal.

Perceptibleistheleastspecific:Afterquiteaperceptiblepause,duringwhichheconsultedhisnotes,thelecturercontinued.2024/5/2926《電子信息工程專業英語教程（第5版）》Perceptibleinuse

perceptiblepalpableappreciablenoticeablediscernible.Palpableappliesbothtowhatisperceptiblebymeansofthesenseoftouchandtowhatisreadilyperceivedbythemind:Ifeltasifmysoulweregrapplingwithapalpableenemy.Whatisappreciableiscapableofbeingestimatedormeasured:Appreciableamountsofnoxiouswastearestillbeingdumpedintotheharbor.2024/5/2927《電子信息工程專業英語教程（第5版）》Perceptibleinuse

perceptiblepalpableappreciablenoticeablediscernible.Noticeablemeanseasilyobserved:noticeableshadowsunderhereyesanoticeabletremorinhisvoice.

Discerniblemeansdistinguishable,especiallybythefacultyofvisionortheintellect:Theskylineiseasilydiscernibleevenatadistanceofseveralmiles.Thenewspaperreportsnodiscernibleprogressinthenegotiations.2024/5/2928《電子信息工程專業英語教程（第5版）》Transmissionindictionary

Theactorprocessoftransmitting.

傳送Thefactofbeingtransmitted.

被轉送的狀態Something,suchasamessage,thatistransmitted.

被轉送的事物Anautomotiveassemblyofgearsandassociatedpartsbywhichpoweristransmittedfromtheenginetoadrivingaxle.

傳動裝置Thesendingofasignal,picture,orotherinformationfromatransmitter.

播送2024/5/2929《電子信息工程專業英語教程（第5版）》Transmissionindictionary

Thesendingofdatafromoneplaceforreceptionelsewhere.

數據傳送Thedispatchingofasignal,message,orotherformofintelligencebywire,radio,telegraphy,telephony,facsimile,orothermeans.

發送消息2024/5/2930《電子信息工程專業英語教程（第5版）》TransmissionintextCD-qualityaudiorequiresatransmissionbandwidthof1.411Mbps.Clearly,substantialcompressionisneededtomaketransmissionovertheInternetpractical.Forthisreason,variousaudiocompressionalgorithmshavebeendeveloped.CD音質的音頻信號需要1.411Mbps的傳輸帶寬。顯然，如果要實現（CD音質音頻信號的）網絡傳輸，就需要進行實質性的壓縮。這樣，就有各種各樣的語音壓縮算法開發出來了。

2024/5/2931《電子信息工程專業英語教程（第5版）》Transmissioninuseasynchronoustransmission異步傳輸broad-bandtransmission寬帶傳輸cabletransmission電纜傳輸diplextransmission雙工傳輸directivetransmission定向發射2024/5/2932《電子信息工程專業英語教程（第5版）》Transmissioninusedistortionlesstransmission無失真傳輸heattransmission熱傳導powerlinecarriertransmission電力線載波傳送transmissionofdigitalTV數字電視(信號)傳輸2024/5/2933《電子信息工程專業英語教程（第5版）》ResolutionindictionaryThestateorqualityofbeingresolute;firmdetermination.

果斷，決意；決心Aresolvingtodosomething.

決定，決議Acourseofactiondeterminedordecidedon.

解決,決定Aformalstatementofadecisionorexpressionofopinionputbeforeoradoptedbyanassemblysuchasthe