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2014年10月16日
Accordingly,wefindthattelephonecircuitsthatrespondwelltothislatterrangeoffrequenciesgivequitesatisfactorycommercialtelephoneservice.
.
Aquantitativewaytoaccountfortheeffectofnoiseistointroducesignal-to-noiseratio(SNR),
-valuedfunctionoftimethatplaystheroleoftheindependentvariable;ateveryinstantoftime,-dimensional,asinthecaseofspeech,music,orcomputerdata;two-dimensional,asinthecaseofpictures;three-dimensional,asinthecaseofvideodata;andfour-dimensional,,weelaborateondifferentsourcesofinformation.
(1),thespeechcommunicationprocessinvolvesthetrans
ferofinformationfromaspeakertoalistener,whichtakesplaceinthreesuccessivestages:
(1)'smindisrepresentedbyaspeechsignalthatconsistsofsounds(.,pressurewaves)generatedinsidethevocaltractandwhosearrangementisgovernedbytherulesoflanguage.
(2),reachingthelistener'sears.
(3),therebycompletingthechainofeventsthatculminate[达到顶点]inthetransferofinformationfromthe
speakertothelistener.
Thespeech-productionprocessmaybeviewedasaformoffiltering,-sectionalarea,beginningattheglottis(.,theopeningbetweenthevocalcords),thespectrum(.,frequencycontent)isshapedbythefrequencyselectivityofthevocaltract;(.,thedistributionoflong-termaveragepower
versusfrequency),however,,thetypeofcommunicationsystembeingconsideredhasanimportantbearingonthebandoffrequenciesconsideredtobe"essential",asmentionedpreviously,abandwidthof300to3100Hzisconsideredadequateforcommercialtelephoniccommunication.
(2)Thesecondsourceofinformation,music,originatesfrominstrumentssuchasthepiano,violin,,,musichastwostructures:,,amusicalsignaldiffersfromaspeechsignalinthatitsspectrumoccupiesamuchwiderbandoffrequenciesthatmayextenduptoabout15
,musicalsignalsdemandamuchwiderchannelbandwidththanspeechsignalsfortheirtransmission.