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1、第二讲多媒体处理理论及共性技术基础信号的数字化理论主要媒体形式介绍信号的线性变换技术信号的统计编码技术多媒体系统特点WhyDigital?Universalstorage,transmissionformatCD,internetPrecision(Rangeofvalues,numberofbits,floatingpoint)Losslesstransmission/storageBUT:samplingratedistortsinformationsizerequirementsmaybe‘large’comparedtoanalogDigitizationProcessSampling
2、fromananalogsignalSamplingErrorsrelatetosignalfrequenciesQuantizationErrorsSampling:Nyquistsamplingtheorem目的—用最少的时间离散信号样本来精确表示原来的连续信号。Nyquist采样标准—采样频率至少为连续信号带宽的两倍。如果采样频率小于这个标准，就会产生“混叠”现象，即采样后离散信号不能重构原连续信号。NyquistSystem:Quantization:LinearandNon-linearLinearquantization:均匀量化Non-linearquantization:非均匀
3、量化(大信号采用大间隔,小信号用小间隔)举例：图象非均匀量化TypesofmultimediadataTextGraphicsPicture/imageAudioSpeechVideoGeneratedmediaTextASCII,UnicodeFormattedText,RichTextDocumentFormats:Structured:Tex,HTMLPageDescriptions:Postscript,PDFGraphicsObjectscircles,splines,rectangles,linesEditableresize,reshape,move,colorizeSynthe
4、ticImages(Pictures)Fixeddigitizedrepresentationbitmap,colorsperpixelEditableinlimitedwaysretouch,cutandpaste,remapcolors,filter [Photoshoptools]no‘model’ofthethingCapturednotjustfromreallife,clipart,screendumpAudioSoundshear15Hzto20kHzSpeechis50Hzto10kHzSpeechRecognitionItishardtowreckanicebeachIcec
5、reamIscreamSynthesisSpeechMusicMIDIfor127instruments,47percussionsoundsNotes,timingSpeechRecognitionIssuesContinuousvsDiscreteVocabularySizeChannel(Microphone)Environment(LocationofmikeandSpeaker)SpeakerDependent/SpeakerIndependentContext(LanguageModel)Interactivity(DialogModel)AcousticModelingDescr
6、ibesthesoundsthatmakeupspeechLexiconDescribeswhichsequencesofspeechsoundsmakeupvalidwordsLanguageModelDescribesthelikelihoodofvarioussequencesofwordsbeingspokenSpeechRecognitionSpeechRecognitionKnowledgeSourcesSpeechVariationsStyleVariationscareful,clear,articulated,formal,casualspontaneous,normal,r
7、ead,dictated,intimateVoiceQualitybreathy,creaky,whispery,tense,lax,modalContextsport,professional,interview,freeconversation,man-machinedialogueSpeakingRatenormal,slow,fast,veryfastStressinnoise,withi
