In this paper a new method for detection of focus is developed. Speech data consists of German spontaneous speech from several speakers. At present the algorithm uses only the fundamental frequency values. By computing a nonlinear reference line through significant anchor points in the F_{0} course, points of highest prominence are determined. The global recognition rate is 78,5% and the mean recognition rate is 66,6%

Petzold, Anja

Universaar

Strategies for focal accent detection in spontaneous speech

Acronym

Strategies for Focal accentDetection in SpontaneousSpeechAnja PetzoldIKP Universitat BonnReport August August Anja PetzoldInstitut fur Kommunikationsforschung und PhonetikUniversitat BonnPoppelsdorfer Allee  BonnTel	    Fax    email fapegikpunibonndeGehort zum Antragsabschnitt 	Die vorliegende Arbeit wurde im Rahmen des Verbundvorhabens Verbmobilvom Bundesministerium fur Bildung Wissenschaft Forschung und TechnologieBMBF unter dem Forderkennzeichen  IV  D  gefordert	 Die Verantwortung fur den Inhalt dieser Arbeit liegt bei der Autorin	appears in Proc th ICPhS Stockholm  vol  		STRATEGIES FOR FOCAL ACCENT DETECTION INSPONTANEOUS SPEECHAnja PetzoldInstitut fur Kommunikationsforschung und Phonetik University of BonnPoppelsdorfer Allee   Bonn Germanyemail	 apeaslikpunibonndeABSTRACTIn this paper a new method for detection of focus is developed Speechdata consists of German spontaneousspeech from several speakers Atpresent the algorithm uses only the fundamental frequency values By computing a nonlinear reference line throughsignicant anchor points in the F course points of highest prominenceare determined The global recognitionrate is  	 and the mean recognitionrate is  	INTRODUCTIONIn the last years the use of prosodicinformation for support of automaticspeech recognition systems has beenwidely extended Prosodic features canbe determined independently of thesegmental level and therefore can provide recognition modules on higher levels e g morphology syntax semantics with additional help for decisionIn this study prosody shall give help toa semantic recognition module by detecting the focusFocus is dened here as the semantically most important part of an utterance which is in general marked byprosodic means If the focus is markedotherwise for instance by word orderprosody will no longer provide a salientcontribution in this case the focus hasto be derived from the linguistic context On the other hand there are alsoprominent parts of an utterance whichcarry information of less importancefor example exclamations and greetingstereotypesDATAThe speech material consists of dialogues of German spontaneous speechcontaining meeting arrangements supplied within the research projectVERBMOBIL Focused areas in thesedialogues contain information abouttime and place like thursday afternoon in my oce and also judgements like that is ok for me neand so onFocus accents were labelled for  dialogues  turns with one or morephrases  focal accents with  different speakers  female  male bya phonetician i e the present authorthrough acoustic perception The sizeof the focus areas was left variablethere was no restriction to word or syllable boundariesMETHODAlready in earlier investigations the prosodic features of focus were examined for German A corpus of readspeech with isolated sentences containing  grammatical objects wasused A statistical classication procedure discriminant analysis was implemented to decide which of the  objectswas the focused one F maxima andminima of the object phrases and thedierence of their positions on the timeaxis were found as the most signicantfeature variables Duration and intensity were not so important for the decisionThis paper will try to solve focusrecognition by global description of theutterance contour At rst we will justlook at the fundamental frequency F How can we now nd the most prominent parts in the F contour There isno hope that we just take the absolutemaxima we have always to take in account declination i e the fall of fundamental frequency toward the end ofthe utteranceInvestigations of Swedish spontaneous speech  have shown that declination can be controlled by the focal accent It was found that in prefocal position there is no downstepping but after a focal accent downstepping is signicant and characteristic We can suppose a physiological correlate for this eect The physical effort for producing an utterance seems1001502002500 500 1000 1500 2000 2500 3000 3500[F0 in Hz][time in ms]But thursday morning at about nine would be ok for meaber Donnerstag Vormittag so um neun waer’ mir rechtF A F A"nbs1k005a.f0""nbs1k005a.ref"Figure  Utterance of a dialogue with reference line and labelled focus FABut thursday morning at about nine o clock would be ok for meto be not equally distributed The eortremains high until the focus is reachedafter the focus the eort sinks to a signicant lower levelTo examine this feature in Germanspontaneous speech several possibilities for computing a reference line weretested A good description of theseproblems is found in  For our workwe cannot use a linear declination linefor detecting a downfall after a focuswe have to look especially at the extrema of the F courseThe reference line was computedas follows First the F contour waspostprocessed by a special smoothingalgorithm described in  Withoutsmoothing results get worse by about 	 In a second step signicant maxima and minima in a window of  mssize were detected The average valuesbetween the maximum and minimumlines yield the global reference line seeFigure FOCUS RECOGNITIONAccording to the already mentionedSwedish investigations the focus mustbe in the area of the steepest fall in theF course Therefore the points withthe highest negative gradient were determined rst in each utterance Therewas no limitation for the number offocal accents in a sentence or phrasePhrase boundaries were not consideredMinimum length for a fall was set to msStarting from the points of steepestfall how can we now get to the position of focus For the time being weassumed as simplest solution the nearest maximum in this region to be the focus In further experiments we will alsoconsider the relative height and intensity of the maxima perhaps also a kindof duration measureRESULTSIn our data only about  	 ofthe frames pertain to focused segmentsTo take account of this two recognition rates will be displayed rst theglobal recognition rate which denotesthe percentage of correct classicationregardless of focus or not and secondthe mean recognition rate with equalweighting of focused and nonfocusedsegments This is illustrated in table Table  Focused parts and recognition rates in percentNo of Dialogue Focused part Total recognition Recognition forglobal mean focus areas nonfocus areasnk     nka     nkb     nkc     nk     nk     nk     Total     As is shown in table  there are farmore deletions than insertions i e therecognition rate for focus areas is significantly worse than for nonfocus areasBut we have to bear in mind that ina collaboration of a prosody and a semantic recognition module it would beworse to have insertions of focal accentsthan to have deletions Hints to focusedareas shall only be an additional helpfor the semantics  without this help itcan do its work as well But false alarmscould divert semantic analysisThe dierent recognition rates forthe dialogues reect the degree of liveliness In a boring and monotone discussion even human recognizers haveproblems to pick up the most important part of a message So the moreengaged the discussion is the clearermarked are the focal accents No signicant dierences between male andfemale voices could be foundDISCUSSIONResults are still not too satisfactory but in no way disappointing Thephenomenon of signicant downfall after a focus in the F contour appearsto be strong enough to be useful forautomatic focus recognition in Germanspontaneous speech Moreover thereare a lot of possibilities left to optimizethe resultsFirst there is the computation of thereference line Most important is a correct smoothing of the F values Likewise there are a lot of ways to determine the points with the steepest falland to detect the focus starting fromthese pointsSecond we have to think about theproblem of labelling the focus To whichextent the acoustic perception is inuenced by semantic knowledge Dowe get the same results when labellingdelexicalisized speech without semantic information but with intact prosodicstructure It is necessary to make further investigations in this directioncomparisons between dierent humanlabellers should be done as wellAnother open question is how to xthe size of the focus regions As mentioned earlier the size of the focus areas was left variable when labelling thefocus accents Therefore distinction between broad and narrow focus has notbeen made till now As dened in narrow focus is used for contrastive accents just one syllable is in focus andbroad focus represents the normal focused constituent the whole word isput in focus both expressed by a pitchaccent on a syllable At least for DutchSluijter  van Heuven  found thatthere are no acoustic dierences in duration and pitch between a broad and anarrow focus accent It seems that thedistinction for these two kinds of focushas to be made rather at the linguisticthan at the acoustic levelUntil now we did not take intoconsideration syntactic information likephrase boundaries or sentence modality Phrase boundaries could help usto restrict focus determination to single phrases and therefore to divide therecognition taskSentence modality is another important fact Already in  it is shownthat in questions with a nal rising contour the focus cannot be determinedin the same way as in declarative sentences We could expect another increase in recognition rate by separatingquestions and nonquestionsACKNOWLEDGEMENTThis work was funded by theGerman Federal Ministry of Education Science Research and TechnologyBMBF in the framework of the Verbmobil Project under Grant  IV G The responsibility for the contentsof this study lies with the authorREFERENCES Batliner A  Fokus Modusund die gro e Zahl Zur intonatorischenIndizierung des Fokus im Deutschen InH Altmann A Batliner W Oppenrieder Zur Intonation von Modus undFokus im Deutschen Niemeyer Bruce G Touati P  On theAnalysis of Prosody in Spontaneous Dialogue Working Papers Lund University     Gussenhoven C Rietveld T Intonation contours and the prominence of F Peaks Proceedings of theICSLP  in Yokohama    Petzold A  Nachverarbeitung bei der Grundfrequenzbestimmung von Sprachsignalen zur Erfassung von IntonationskonturenFortschritte der Akustik  DAGA    Sluijter A van Heuven V J Eects of Focus Distribution Pitch Accent and Lexical Stress on the Temporal Organization of Syllables in DutchPhonetica    

Scientific documents from the Saarland University,

Strategies for Focal accent
Detection in Spontaneous
Speech
Anja Petzold
IKP Universit

at Bonn
Report 
August 
August 
Anja Petzold
Institut f

ur Kommunikationsforschung und Phonetik
Universit

at Bonn
Poppelsdorfer Allee 
 Bonn
Tel	
    
Fax
    
email
 fapegikpunibonnde
Geh

ort zum Antragsabschnitt 	
Die vorliegende Arbeit wurde im Rahmen des Verbundvorhabens Verbmobil
vom Bundesministerium f

ur Bildung Wissenschaft Forschung und Technologie
BMBF unter dem F

orderkennzeichen  IV  D  gef

ordert	 Die Verant
wortung f

ur den Inhalt dieser Arbeit liegt bei der Autorin	
appears in Proc th ICPhS Stockholm  vol  	
	

STRATEGIES FOR FOCAL ACCENT DETECTION IN
SPONTANEOUS SPEECH
Anja Petzold
Institut f

ur Kommunikationsforschung und Phonetik University of Bonn
Poppelsdorfer Allee   Bonn Germany
email	 ape
aslikpunibonnde
ABSTRACT
In this paper a new method for de
tection of focus is developed Speech
data consists of German spontaneous
speech from several speakers At
present the algorithm uses only the fun
damental frequency values By comput
ing a nonlinear reference line through
signicant anchor points in the F
 
course points of highest prominence
are determined The global recognition
rate is  	 and the mean recognition
rate is 


 	
INTRODUCTION
In the last years the use of prosodic
information for support of automatic
speech recognition systems has been
widely extended Prosodic features can
be determined independently of the
segmental level and therefore can pro
vide recognition modules on higher lev
els e g morphology syntax seman
tics with additional help for decision
In this study prosody shall give help to
a semantic recognition module by de
tecting the focus
Focus is dened here as the seman
tically most important part of an ut
terance which is in general marked by
prosodic means If the focus is marked
otherwise for instance by word order
prosody will no longer provide a salient
contribution in this case the focus has
to be derived from the linguistic con
text On the other hand there are also
prominent parts of an utterance which
carry information of less importance
for example exclamations and greeting
stereotypes
DATA
The speech material consists of dia
logues of German spontaneous speech
containing meeting arrangements sup
plied within the research project
VERBMOBIL Focused areas in these
dialogues contain information about
time and place like thursday after
noon in my oce and also judge
ments like that is ok for me ne
and so on
Focus accents were labelled for  di
alogues  turns with one or more
phrases  focal accents with 
 dif
ferent speakers  female  male by
a phonetician i e the present author
through acoustic perception The size
of the focus areas was left variable
there was no restriction to word or syl
lable boundaries
METHOD
Already in earlier investigations 
the prosodic features of focus were ex
amined for German A corpus of read
speech with isolated sentences con
taining  grammatical objects was
used A statistical classication proce
dure discriminant analysis was imple
mented to decide which of the  objects
was the focused one F
 
maxima and
minima of the object phrases and the
dierence of their positions on the time
axis were found as the most signicant
feature variables Duration and inten
sity were not so important for the deci
sion
This paper will try to solve focus
recognition by global description of the
utterance contour At rst we will just
look at the fundamental frequency F
 

How can we now nd the most promi
nent parts in the F
 
contour There is
no hope that we just take the absolute
maxima we have always to take in ac
count declination i e the fall of fun
damental frequency toward the end of
the utterance
Investigations of Swedish sponta
neous speech  have shown that dec
lination can be controlled by the fo
cal accent It was found that in pre
focal position there is no downstep
ping but after a focal accent down
stepping is signicant and characteris
tic We can suppose a physiological cor
relate for this eect The physical ef
fort for producing an utterance seems
100
150
200
250
0 500 1000 1500 2000 2500 3000 3500
[F0
 in 
Hz
]
[time in ms]
But thursday morning at about nine would be ok for me
aber Donnerstag Vormittag so um neun waer’ mir recht
F A F A
"nbs1k005a.f0"
"nbs1k005a.ref"
Figure  Utterance of a dialogue with reference line and labelled focus FA
But thursday morning at about nine o clock would be ok for me
to be not equally distributed The eort
remains high until the focus is reached
after the focus the eort sinks to a sig
nicant lower level
To examine this feature in German
spontaneous speech several possibili
ties for computing a reference line were
tested A good description of these
problems is found in  For our work
we cannot use a linear declination line
for detecting a downfall after a focus
we have to look especially at the ex
trema of the F
 
course
The reference line was computed
as follows First the F
 
contour was
postprocessed by a special smoothing
algorithm described in  Without
smoothing results get worse by about
 	 In a second step signicant max
ima and minima in a window of  ms
size were detected The average values
between the maximum and minimum
lines yield the global reference line see
Figure 
FOCUS RECOGNITION
According to the already mentioned
Swedish investigations the focus must
be in the area of the steepest fall in the
F
 
course Therefore the points with
the highest negative gradient were de
termined rst in each utterance There
was no limitation for the number of
focal accents in a sentence or phrase
Phrase boundaries were not considered
Minimum length for a fall was set to
 ms
Starting from the points of steepest
fall how can we now get to the posi
tion of focus For the time being we
assumed as simplest solution the near
est maximum in this region to be the fo
cus In further experiments we will also
consider the relative height and inten
sity of the maxima perhaps also a kind
of duration measure
RESULTS
In our data only about  	 of
the frames pertain to focused segments
To take account of this two recogni
tion rates will be displayed rst the
global recognition rate which denotes
the percentage of correct classication
regardless of focus or not and second
the mean recognition rate with equal
weighting of focused and nonfocused
segments This is illustrated in table 
Table  Focused parts and recognition rates in percent
No of Dialogue Focused part Total recognition Recognition for
global mean focus areas nonfocus areas
nk    

 
nka  
 

  
nkb    
 
nkc  
   
nk 
 
 

  
nk   
 
 
nk 

    
Total   



  
As is shown in table  there are far
more deletions than insertions i e the
recognition rate for focus areas is signif
icantly worse than for nonfocus areas
But we have to bear in mind that in
a collaboration of a prosody and a se
mantic recognition module it would be
worse to have insertions of focal accents
than to have deletions Hints to focused
areas shall only be an additional help
for the semantics  without this help it
can do its work as well But false alarms
could divert semantic analysis
The dierent recognition rates for
the dialogues reect the degree of live
liness In a boring and monotone dis
cussion even human recognizers have
problems to pick up the most impor
tant part of a message So the more
engaged the discussion is the clearer
marked are the focal accents No sig
nicant dierences between male and
female voices could be found
DISCUSSION
Results are still not too satisfac
tory but in no way disappointing The
phenomenon of signicant downfall af
ter a focus in the F
 
contour appears
to be strong enough to be useful for
automatic focus recognition in German
spontaneous speech Moreover there
are a lot of possibilities left to optimize
the results
First there is the computation of the
reference line Most important is a cor
rect smoothing of the F
 
values Like
wise there are a lot of ways to deter
mine the points with the steepest fall
and to detect the focus starting from
these points
Second we have to think about the
problem of labelling the focus To which
extent the acoustic perception is in
uenced by semantic knowledge Do
we get the same results when labelling
delexicalisized speech without seman
tic information but with intact prosodic
structure It is necessary to make fur
ther investigations in this direction
comparisons between dierent human
labellers should be done as well
Another open question is how to x
the size of the focus regions As men
tioned earlier the size of the focus ar
eas was left variable when labelling the
focus accents Therefore distinction be
tween broad and narrow focus has not
been made till now As dened in 
narrow focus is used for contrastive ac
cents just one syllable is in focus and
broad focus represents the normal fo
cused constituent the whole word is
put in focus both expressed by a pitch
accent on a syllable At least for Dutch
Sluijter  van Heuven  found that
there are no acoustic dierences in du
ration and pitch between a broad and a
narrow focus accent It seems that the
distinction for these two kinds of focus
has to be made rather at the linguistic
than at the acoustic level
Until now we did not take into
consideration syntactic information like
phrase boundaries or sentence modal
ity Phrase boundaries could help us
to restrict focus determination to sin
gle phrases and therefore to divide the
recognition task
Sentence modality is another impor
tant fact Already in  it is shown
that in questions with a nal rising con
tour the focus cannot be determined
in the same way as in declarative sen
tences We could expect another in
crease in recognition rate by separating
questions and nonquestions
ACKNOWLEDGEMENT
This work was funded by the
German Federal Ministry of Educa
tion Science Research and Technology
BMBF in the framework of the Verb
mobil Project under Grant  IV 
G The responsibility for the contents
of this study lies with the author
REFERENCES
 Batliner A  Fokus Modus
und die gro e Zahl Zur intonatorischen
Indizierung des Fokus im Deutschen In
H Altmann A Batliner W Oppen
rieder Zur Intonation von Modus und
Fokus im Deutschen Niemeyer
 Bruce G Touati P  On the
Analysis of Prosody in Spontaneous Di
alogue Working Papers Lund Univer
sity 
   
 Gussenhoven C Rietveld T 
Intonation contours and the promi
nence of F
 
Peaks Proceedings of the
ICSLP  in Yokohama   
 Petzold A  Nachverar
beitung bei der Grundfrequenzbestim
mung von Sprachsignalen zur Erfas
sung von Intonationskonturen
Fortschritte der Akustik  DAGA 
  
 Sluijter A van Heuven V J 
Eects of Focus Distribution Pitch Ac
cent and Lexical Stress on the Tempo
ral Organization of Syllables in Dutch
Phonetica    


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Strategies for focal accent detection in spontaneous speech

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Acronym

Scientific documents from the Saarland University,