Text-based and Signal-based Prediction of Break Indices and Pause Durations
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Text-basedandSignal-basedPredictionofBreakIndicesandPauseDurations
HartmutR.Pfitzinger&UweD.Reichel
InstituteofPhoneticsandSpeechCommunication
UniversityofMunich,Germany
{hpt;reichelu}@phonetik.uni-muenchen.de
Abstract
Therelationbetweensymbolicandsignalfeaturesofprosodic
boundariesisexperimentallystudiedusingpredictionmethods.
Text-basedbreakindexpredictionturnsouttobefairlygood,
butsignal-basedpredictionandpausedurationpredictionper-formworse.Apossiblereasonisthatrandomsignalfeature
variations,asusuallyproducedbyhumans,arehardtopredict.
1.Introduction
Speakersdividetheirutterancesintoprosodicphrasesseparated
byweakorstrongprosodicboundaries.Theseboundariescan
beperceptuallyclassifiedaccordingtotheToBIbreakindices,
ortheycanbedescribedbymeasurementsofprosodicfeatures
ofthespeechsignal,i.e.thepausedurationandthelocalcon-toursofF0,speechrate,amplitude,andvoicequalityinthe
vicinityoftheprosodicboundary.Thegoalofthepresentstudy
istoinvestigatetherelationshipbetweensymbolicandsignal
representationsofprosodicboundariesbymeansofthreepre-dictionmethods(seeFig.1).
Prosodicphrasebreakpredictioncanbedecomposedinto
twotasks:breaklocalizationandpredictionofitsphoneticreal-
ization.Forthelatterthisstudyconcentratesonpauseduration.Rule-basedorstatisticalapproachestacklebothtasksbyex-
ploitingpartofspeech(POS),syntactical,andrhythmicalinfor-
mation.Forrule-basedbreaklocalizationLiberman&Church
[9]usethefact,thatcertainPOSclassesoccurpreferablyphraseinitially(chinks)whileothersdonot(chunks).Gee&Grosjean
[7]andBachenko&Fitzpatrick[2]imposesyntacticallymoti-
vatedperformancestructuresonanutterance.Thedistanceof
twoadjacentwordsinthesestructuresgivenintheleveloftheircommonnodedeterminesthebreakstrengthandthusthepause
durationbetweenthesewords.Therule-basedKeller-Zellner
algorithm[19]alsoincorporatesrhythmicalconstraints.
InsomestatisticalapproachesphrasebreaksarepredictedfromagivenpartofspeechsequencebyamodifiedMarkov
Tagger.Forexample,Black&Taylor’stagger[3]isbased
onconditionalemissionprobabilitiesforPOSsequencesco-
occurringwiththebreaktypegivenatthecorrespondingstateandconditionaltransitionprobabilitiesofthisbreaktypefora
givenbreaktypehistory.Others(e.g.[1])useclassificatorsas
CART[4]inordertopredictphrasebreaksandpauselengths
fromasetoflinguisticfeaturesaspartofspeechandwordandsyllabledistances.CARTsarewellsuitedforthistaskdueto
theirabilitytocopewithcategoricalandcontinuoustypesof
dependentandindependentvariables.
In2002,Mixdorff[11]investigated,amongotherprosodic
properties,pausedurationsintheIMSRadioNewsCorpus[15].Meanvaluesandstandarddeviationsofpausesatsen-
tenceboundarieswere716msand336ms,respectively,andof
pauseswithinsentenceswere327msand132ms,respectively.2.Method
Weinvestigatedthepredictabilityofbreakindicesandpausedu-
rationsbytext-basedandbysignal-basedfeatures(seeFig.1).
Inordertoaccountforhumandurationperception,pausedu-
rationswererepresentedonalogarithmicscale.ForbreakindexpredictionweusedC4.5decisiontrees[14],forpause
durationsCARTs(classificationandregressiontrees[4])pro-
videdbyR.Additionally,weanalysedthecorrelationbetween
prosodicmeasuresandpauseduration.
2.1.Data
ThepresentstudyisbasedontheIMSRadioNewsCorpus[15]whichconsistsofGermannewstextsreadbyprofessional
speakers.Originally,thedataisautomaticallysegmentedinto
phonemesaccordingtotheGermanSAM-PAinventoryfol-
lowedbysomemanualrefinements.ProsodyofthedatawasmanuallylabelledfollowingtheGToBIconventions[10].
Priortoanalysisofthedataasubstantialcorrectionwas
necessary.Weomittednewsrepetitionsandmanuallycorrected
thephoneboundariesinordertoachievereliablepausedura-tionandPLSRmeasures(perceptuallocalspeechrate[12,13]).
Particularly,wereplacedcanonicaltranscriptionsbytheiractual
phoneticrealizations,insertedglottalstops,whichhaveunfortu-
natelybeenabsent,andreplaced/Vowel/-/R/-pairsbytheircor-responding/Vowel/-/6/-diphthongs,especially/@/-/R/by/6/.
Finally,ourdatacomprises28newsarticlesreadbyone
malespeaker.Itconsistsof16285phones,2384wordtokens,
and970wordtypes,whichisapproximatelyhalfoftheorigi-naldata.Fortext-basedpredictionallfinalwordsofeachsig-
nalwereexcluded,becausesubsequentpausedurationnaturally
couldnotbemeasured.80%ofthisdatawereusedfortraining
andtheremainderastestset.Thedataforn-gramandcollo-cationmodelingcomesfromdiversewrittennewscorporaand
consistsof327821wordtokensand42741types.
CARTCART(Part of Speech, Position, Cohesion)
C4.5
S I G N A L SBreak Indices
Pause Durations
Lin. RegressionC4.5S Y M B O L S
(Prosodic Contours of Intonation, Speech Rate, Amplitude)
Figure1:Text-based(top-down)andsignal-based(bottom-up)
predictionsofbreakindicesandpausedurationsinthisstudy.CategoricaldataarepredictedbyC4.5decisiontrees,andcon-
tinuousdatabyCARTsorbylinearregression.