Difference Limens for f0

8/12/2019 Difference Limens for f0

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Difference limens for fundamental frequency contoursin sentences

M.S. Harris

Psychology epartment, Kean College f New Jersey, Union, New Jersey 7083

N. Umeda

Department f Linguistics, ew York University, 0 Washington lace, New York, New York 10003

(Received 4 May 1984; accepted or publication 18 December 1986)

Difference imens DLs) for fundamental requency Fo) of naturally spoken entences erestudied. The experiments an be classified nto two major categories. n the first category hefundamental requency f a portion of sentences f 2 to 3 s in duration was manipulated. hesecond et of experiments sed very short sentences "The subject erb ") in which the Fo of theentire sentence was manipulated. Across experiments, entences f comparable ength yieldedsimilar DLs, except when he Fo was abruptly shifted within a continuous oicing period.However, he DLs did vary significantly s a function of stimulus omplexity nd speaker. herange of DLs obtained n this series f experiments as between 10 and 50 times greater hanthat found with sustained ynthetic vowels.

PACS numbers: 43.71.Es, 43.66.Fe

INTRODUCTION

Numerous tudies ave nvestigated he sensitivity fhuman isteners o differences n frequency of pure tones(e.g., Harris, 1952;Rosenblith nd Stevens, 953). Withpure ones t is very asy ocontrol ll aspects f he stimuli.Harris (1952) and others have shown hat, for pure tones,frequency ifference imens f ess han 1 Hz are not uncom-mon. The actual DLs were dependent n the subjects sed,the methodology mployed, nd he "loudness evel" LL)of the tones.

Generalization rom pure ones o speech s, of course,impossible. lanagan ndSaslow 1958), n a now classicstudy, eported esults f an experiment n which hey mea-sured he DL for fundamental requency Fo) of syntheticvowel timuli with steady o. The average L for six highlytrained subjects cross number f vowels was 0.32 Hz.They claimed hat heir isteners ere ble o make lightlymore acute discriminations f changes n Fo of vowels hanof pure tones of equivalent requency nd level. Klatt(1973), using he synthetic owel/e/, compared he DLsfor steady o,a ramp o, and a steep ate ofFochange, laim-ing hat he synthetic owelwithsteady odid not have he"dynamic ualities haracteristic fspeech" p. 8). The DLfor he steady owas .3 Hz, which was ery similar o thatfound y Flanagan ndSaslow. or he amp Fo he DL was2 Hz, and or he "steep ate of change f Fo" (32 Hz/s) theDL was 4 Hz. Klatt assumed hat the steep ate of change fFowas closer o speech n quality. he results rom Klatt'sstudy uggest hat with speechlike timuliwith changing o,the DL for Fomay be an order f magnitude igher han t isfor stimuli with steady Fo.

There are studies which have used more complex stimu-li than those mentioned above, such as consonant-boundvowels (Mermelstein, 1978) and multisyllabic numberwords ('t Hart, 1974, 1981). However, no data from natu-

rally spoken sentences re available. The current experi-ments were designed o fill this gap. Although we were awareof the many difficulties nvolved n conducting frequencyDL experiment using complex speech timuli, we felt thatsuch an investigation as necessary ecause f the dearth ofrelevant psychoacoustic ata.

The current investigation onsists f four experiments.Untrained subjects were used n all of the experiments norder to obtain a large number of subjects. n the first twoexperiments, ubjects iscriminated hanges n Fo of about750-ms duration nside a sentence f approximately 000-ms

duration. In the last two experiments, horter sentences(600-800 ms) were used, and the Fo of the entire sentencewas raised or lowered. Prior to these our experiments,pilot study was conducted o see f phonemic nformationaffected he DL for the Fo of a sentence. n this pilot studysubjects articipated n two sessions, ne with all linguisticinformation n the sentence ntact and the other with phone-mic nformation of the same sentence estroyed y changingthe value of all LPC coefficients. o significant differencewas obtained between the results from the two sessions, nd,therefore, entences ith phonemic nformation ntact wereused hroughout he four experiments.

I. GENERAL METHODSDifferent stimuli were used n each of the four experi-

ments n this study. Since he stimulus preparation proce-dures were dentical and the experimental rocedures erethe same n all experiments, general procedures re dis-cussed in this section. Table I summarizes the differences

between experiments.The procedure or making stimuli was as ollows: First,

sentences ere recorded on analog ape and then digitizedon a Data General Eclipse computer. Fundamental requen-cy values of the sentence ere obtained using a parallel pro-

1139 J. Acoust. oc.Am. 1 4), April 987 0001-4966/87/041139-07500.80 1987 Acoustical ociety fAmerica 1139

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TABLE I. Summary of differences etween xperiments.

No. of No. of Sentence Portion of Fo Control of F oExp. sentences speakers length change change

Step of Fo No. ofchange n Hz listeners

I 5 I(MH)

II 4 2(MH,PB)

III(a) 4 I(MH)III(b) 1 3 (RC,DM,JW)IV 1 4(MH,RC, DM,

JW)

2-3 s middle of the nonesentence

2-3 s middle of the change tarts and endssentence at stop consonants

6-800 ms entire sentence none6-800 ms entire sentence none6-800 ms entire sentence none

5 2O

5 19

3 172 19

3 for MH, 192 for others

cessing echnique Gold and Rabiner, 1969). An LPC vo-coder program (Atal and Hanauer, 1971) was used tomanipulate Fo values: The sentence was analyzed irst andthen resynthesized with original or with shifted Fo values(e.g., + 3 Hz, -- 10 Hz, etc.).

Only male speakers ere used. A stimulus onsisted f asentence resented wice, once with original Fo values andthe other time with shifted Fo values including a zero shiftcondition) or the designated ortion of the sentence. n oth-er words, the whole Fo contour during that portion wastransposed pward or downward by the specified mount.

The position of the standard entence nd he Fo-shiftedone in the pair was counterbalanced, o that the standardsentence ppeared n the first position he same number oftimes s t did n the second osition n a listening ession.The presentation f all of the stimuli in the session was inrandom order.

Subjects n each experiment were either college or highschool tudents nd were either paid or given course redit nan introductory psychology lass. All reported having nohearing problems. hey were ested n groups f five o sevenin a large Industrial Acoustics Corporation sound booth.They were nstructed o put on a set of headphones nd toldthat they would hear a certain number of pairs of sentences.They were to judge for each pair whether he second en-tence ontained ny portion hat was higher or ower n pitchthan the first. They were asked o guess f they were not sure.The within-pair nterval was 0.55 s, and the between-pairinterval was 2.55 s.

Prior to the actual est sentences, hey heard several en-tence pairs n order o familiarize hemselves ith the ype ofstimuli and the testing situation.

TABLE II. List of sentences nd their DLs for experiment . The portionwhose o was changed s n italics. The DL is the 75% correct point on thepsychometric unction.

DL(Hz)Sentence Down Up

( 1 I am not going o get rid of my pet. 7.5 < 5(2) We must all live together. 11.5 8(3) It is an unusual situation, I admit. 14.5 16(4) To begin with, pigs are very beautiful animals. 11.5 15(5) The ordinary olk left no trace. 10 8.5

II. EXPERIMENTS WITH LONGER SENTENCES

A. Experiment IL Method

a. Stimuli. A male speaker MH read a number of sen-tences aken rom a variety of texts. Five sentences ere cho-sen or use n this experiment; hey are isted n Table I. TheFo of a portion of each sentence in parentheses) aschanged n 5-Hz steps n both ncreasing nd decreasing i-rections. igure 1 s an example f the ype of changes hatwere made. There were four changes f 5 Hz each n theupward direction nd four changes n the downward direc-tion from the original Fo contour. The dashed ine above trepresents 5-Hz parallel ncrease n the portion of the sen-tence hosen or change. he dashed ine below epresentsthe same hange n the downward irection. he duration ofthe changed ortionwas etween 25and 825msdependingupon he sentence. ll changes ere made n a medial por-tion of the sentence hat included a stressed word. Two stim-ulus tapes were created on which pairs of sentences ererecorded n random order. Each possible air appeared ourtimes on each ape, twice with the standard irst and twicewith the standard econd. ach ape contained 80 pairs ofsentences. he stimuli on each ape had a different andomorder but were otherwise identical.

b. Procedure. wenty college tudents ere ested n two

200. ,

/ '1 " ...

/550 THE INARYOLKo soo

LEFT NO TRACE.I

1500 2000

TItlE (ms)

FIG. 1. llustration of the ype of Fo contour hanges made n the sentences.The dashed ines epresent -Hz upward and downward hanges rom heoriginal contour.

1140 J. Acoust. Soc. Am., Vol. 81, No. 4, April 1987 M.S. Harris and N. Umeda: Fundamental requency ontours 1140



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sessions, alf receiving ape 1 first and half receiving ape 2first. The sessions ere separated y 1 week.

The psychometric unctions or both upward and down-ward changes rom the original Fo were plotted and he DLswere determined from the functions. The DL was defined as

the 75% correct point (obtained by linear interpolation)which has been raditionally used when the method of con-stant stimuli s employed. The data were analyzed using atwo-way repeated-measures nalysis of variance n whichthe effect of the direction of change and differences mongsentences were examined.

The results of the first session ere compared o those ofthe second session using a t test in order to determinewhether here was any practice effect.

2. Results

Figure 2 shows he psychometric unctions or the fivesentences. ach point in the figure represents he mean of 8judgments or all 20 subjects the mean of 160 udgments).The five sentences nd their respective DLs are shown nTable II. The results of a 2 X 5 factorial analysis of varianceindicated hat there was no significant ffect of direction of

change. That is, there were no differences etween he up-ward and downward shifts of Fo. There were, however, sig-nificant differences among sentences, (4,76) = 10.38,p


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450

4OO

350

300

250

200

150

I O0

50

500I I i

1000 1500 2000

TIHE (ms)

FIG. 3. Fundamental requency lot or a sentence The water was buoyantand cold" n experiment . Vertical ines ndicate egion of change.

go

8o

m 70

o

4 0000000 e

_;. ...'- ',,,,.,,c---.';.-...'":"-'""-'?" '- 4'

SPEAKER PB

I I I I i3 6 9 12 15

FREQUENCY DIFFERENCE IN Hz

onset or offset cue (i.e., an abrupt change n continuous omovement) would be eliminated. An example of a sentenceand the location of the Fo change re shown n Fig. 3.

b. Procedure. n this experiment, -Hz steps were usedbecause n one sentence f experiment the DL was ess han5 Hz. There were 5 changes made, so hat the greatest iffer-ence between stimuli was 15 Hz. In order to simplify theprocedure, o "down" condition was used, because he re-sults of experiment indicated hat direction of change wasnot a significant eterminant f the DLs obtained.

Thirty-eight paid high school seniors istened o 192pairs of sentences. ineteen ubjects eard speaker MH and19 subjects eard speaker B. Each possible air was pre-sented ight imes n a counterbalanced andom order.

Psychometric unctions or both speakers ere plottedand the DLs were determined. The average percent correctscores ere analyzed sing 2 X 4 mixed design nalysis fvariance o assess he effects f speakers nd sentences.

2, Results

The psychometric unctions or each speaker re shownin Fig. 4. The most notable inding n comparing hese wosets of functions s the average percent correct or the twospeakers. n fact, etaining our operational efinition f DL,the curves or speaker PB do not reach hreshold with theexception of sentence . The DLs for speaker MH rangedfrom 10.5 Hz to over 15 Hz (8% to 11% ofthe averageFo orspeaker MH). The mean of the DLs for MH was arger hanthat found n experiment .

The results f the analysis f variance ndicated signifi-

cant difference n the isteners' erformance s a function ofspeaker, F(1,36) = 5.67, p 15 > 1510.5 > 1511.25 > 1512.75 12

1142 J. Acoust. Soc. Am., Vol. 81, No. 4, April 1987 M.S. Harris and N. Umeda: Fundamental requency contours 1142



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movements. herefore, t is reasonable o assume hat sub-jects re ess ensitive o Fo differencesn naturally pokensentences han o inearly hanging o n synthetic owels. tmust be remembered, owever, hat the subjects sed n ourexperiments ereuntrained, n contrast o the subjects fearlier studies.

Another nterpretation or he arge Ls n ourstudy sthat the subjects were not told where n the sentence heywere supposed o compare he height of Fo in the pair ofstimuli and, therefore, hey had no obvious lace n the sen-tence o anchor heir judgment. The larger DLs of experi-ment I suggest hat this nterpretation s plausible. hat is,the onset and offset of Fo manipulation n the sentence werecontrolled n experiment I but not n experiment . In otherwords, some of the sentences sed n experiment containedan extra cue or the ocation of onset or offset f Fo manipula-tion, this being he discontinuity n Fo contour. This cue wasabsent n all sentences n experiment I. The difference mayhave made he DLs for speaker MH in experiment I higherthan those obtained n experiment .

The speaker ifference n experiment I was arge, and sstatistically ignificant. his finding poses dditional ques-tions. s this difference ue to the difference n acoustic ig-nals attributable o the speaker r to the analysis nd synthe-sis echnique mployed n the study? MH's voice had rathermonotonous itch, while n PB's voice, pitch varied n a larg-er range. At the same ime, the LPC process s known tocreate distortion, and the degree of distortion s speaker e-pendent. n fact, MH's voice after he LPC process etainedits original quality better than PB's voice.

The experiments described n the following sectionswere concerned with the questions aised n experimentsand II. Experiment II (a) was designed o answer he ques-tion of whether simpler stimuli would yield smaller DL val-ues, and experiment III(b) addressed he question of

whether the speaker difference was reliable.III. EXPERIMENTS WITH SHORTER SENTENCES

A. Experiment III

1. Experiment Ill(a)

a. Stimuli. In the current experiment, hanges n Fo hatencompassed he entire sentence erved as the stimuli. Thesentences ere short and composed f three monosyllabicwords, hat is "the," a noun as subject, nd a verb (e.g., "thetrain moved"). Four such simple sentences ere read by onespeaker, MH. The procedure or the preparation of the stim-uli was dentical o the previous experiments. he Fo of theentire sentence as changed n 3-Hz steps n the increasingdirection only. There were a total of five steps.

b. Procedure. eventeen igh school tudents articipat-ed in the experiments. ach subject udged 288 pairs of sen-tences. he data were analyzed using an analysis of varianceto examine f there is a significant difference between sen-tences.

c. Results. igure 5 shows he psychometric unctions ofthe our sentences or speaker MH. An average DL of 4.8 Hzwas obtained. This value s far smaller han any DL obtainedin experiments and II. Analysis of the results also revealedno significant ifferences etween he sentences.

o3 6 9 12 15


FIG. 5. Psychometric unctions or speaker MH in experiment II (a).

2. Experiment Ill(b)

a. Stimuli. Since here was no statistically significantdifference n the DLs of the four sentences, one of the four,"the boy talked," was used n this experiment. Three newmale speakers were used. The experimental rocedure wasidentical to experiment III(a) except that the Fo waschanged n 2-Hz steps. The maximum range of Fo changewas 10 Hz.

A stimulus ape consisting f pairs of sentences wascreated or each of the three speakers. ach possible airappeared 4 times on each ape. Each tape contained 144pairs of the sentence.

b. Procedure. Nineteen college students were ested overthree sessions uring each of which they heard he tape ofone speaker. he order of administration f the tapes wascounterbalanced so that each third of the listeners heard a

different order of speakers. he experiment was conductedover a 3-week period. The listeners eard one speaker achweek.

The DLs were analyzed using an analysis f variance oexamine he hypothesis hat there s a significant ifferencein DL between peakers. he psychometric unction or eachspeaker was plotted and the DLs were determined romthose functions.

c.Results. igure shows he'psychometricunctionsfor the hree speakers. ach point n the figure epresents hemean of 24 judgments or all 19 listeners the mean of 456judgments). t is clear rom nspection f the figure hat theperformance f the isteners aried as a function of speakers.The difference n DL between peakers as statistically ig-nificant, F(2,54) = 9.84, p < 0.01. Individual comparisonsbetween he mean DLs for the three speakers howed hatthe overall significance was due to the difference betweenspeaker W and the other wo speakers. he DL for speakerJW was 3.25 Hz, for RC the DL was 7.0 Hz, and for DM itwas greater han 10 Hz.

The results of this experiment how a large difference nlisteners' bility to udge undamental requency hanges na sentence s a function of the speaker. t is interesting onote that if the data from experiment II (a) were included,the findings would be even more intriguing. n experimentIII (a), in which the same sentence was one of the stimuli




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ioo

9o

60-

50-

40-

$0-

eeee eeeeeeeee

JWRC DM .........

0 2 4 6 B I0


FIG. 6. Psychometric unctions or the hree speakers n experiment II (b).

used, he DLs for speaker H were 4 Hz for that sentence.Examination f the results or all speakers howed airlyacute requency iscrimination or wo of the speakers JW,3.25 Hz and MH, 4.0 Hz). The other two showed substan-tiallypoorer iscrimination 7.0Hz for RC and greater han10Hz for DM). The question hat arises s: What s here nthe speech fa particular peaker hat makes t easy r diffi-cult for a listener o detect Fo changes? t is possible hatthere is some acoustic characteristic that is common to thespeech fMH and JW hat s not present n he speech f heother wo speakers r vice versa. Further nvestigation srequired o determine hat his characteristic ightbe.

B. Experiment IV

The fourth experiment was designed o determine heeffect of the computer rocessing ystem n the DL for thespeakers sed n experiment II. The stimuli used n experi-ments II (a) and (b) were urther processed sing an algo-rithm or spectral orrection f LPC processed peech evel-oped by Malah (1981, 1982). The testing procedure wasidentical o that described bove. The two experiments werecompared n order o see f there were significant L differ-ences s a function of the processing ethod. Nineteen paidvolunteers listened to these stimuli. These listeners had not

participated n any of the previous xperiments.

a. Results. The mean DL values or each speaker werecompared cross xperiments II and IV. The t tests wereperformed n order o determine f any significant hange nDLs occurred as a function of the processing method. Theonly significant difference was for speaker RC. For hisspeech, with the spectral correction method, here was aconsiderable ecrease n DL, t(35) = 2.01, p < 0.05. For thespectrally orrected peech f experiment V, the DL forspeaker DM was significantly igher han for either of theother wo speakers. MH's results ould not be ncluded nthe across peaker tatistical omparisons, ecause he stim-uli of his speech ere changed n 3-Hz steps, nd hat of theother three speakers n 2-Hz steps.)

C. Discussion of experiments III and IV

The results obtained rom experiments II and V are asfollows: 1) A significant peaker difference n Fo DL wasobserved; nd (2) the spectral orrection f LPC processedspeech Malah, 1981, 1982) decreased he DL for only oneof our four speakers.

Malah's technique f restoring he spectral nvelope fLPC-processed peech (i.e., restoring higher frequency

components) rings back he quality of the original voice oan extent, but not to a satisfactory egree. t is premature oconclude hat the decrease n DL values n RC's speech, nthe spectrally orrected ersion, s the consequence f therestoration f higher requency omponents this conclu-sion would of necessity mply that higher requency ompo-nents lay an active ole n the udgment f Fo). Since here sno convenient echnique o manipulate o contour f spokensentences ther than the LPC vocoder, t present he ques-tion concerning he influence f voice quality on the DL.judgments emains unanswered.

Large differences n D L values among speakers mayalso be attributed to the difference in acoustic characteristics

of their speech. he Fo contours display arge differencesamong ur speakers. ll of them display rise mmediatelyafter/b/in "boy" until near he end of the vowel, and a fallthrough he word "talked." Table V summarizes he aver-age Fo, the amount and the ratio of the rise and the fall,together with the ength of the utterance excluding/kt/atthe end of the sentence), nd the F o range or each speaker.The rise or any speaker s far less teep han the fall. How-ever, he rise s nearly wice (for MH) to more han six imes(for DM) steeper han the steep o change 32 Hz/s) for asynthetic owel n Klatt's (1973) study. The surprising act

TABLE IV. Fundamental requency haracteristics f the our alkers n the utterance The boy alked."

[ t ] in BOYLowest Highest

Average Fo n the Fo n the Amount ofTalker Fo (Hz) vowel Hz) vowel Hz) rise Hz)

MH 126 126 134 8JW 125 121 146 25RC 126 129 143 14DM 119 104 139 35

[ ] in TALKEDDuration of Duration of

the vowel Highest o Lowest o Amount of the vowel Total Fo(s) (Hz) (Hz) fall (Hz) (s) range (Hz)

0.14 142 115 27 0.16 270.25 137 105 32 0.18 410.17 141 102 39 0.24 410.18 147 96 51 0.18 51

1144 J. Acoust. oc.Am.,Vol.81, No.4, April 987 M.S. Harris nd N. Umeda: undamental requency ontours 1144



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is that the DLs of our two speakers MH and JW) with thisshort simple sentence exhibit values as small as those inKlatt's study.

The hypothesis f't Hart ( 1981 , that the size of the DLis relative o the average undamental requency, might betrue if the ratio of the average undamental requencies s aslarge as or larger han 2 to 1. However, we have o reject hehypothesis when the difference n the average undamentalfrequencies etween speakers s small. Our result shows hatthe speaker with the lowest average Fo demonstrated helargest DL, and that the DL value varies with the same aver-age Fo. Since Fo changes ts direction and amount constantlyin the sentence timulus, t is impossible o tell if linguisticinformation helps isteners' udgments, r if listeners ried toanchor their judgments at the point where Fo change be-comes minimal (for example, at the point where Fo changesfrom rise to fall). In other words, no simple comparisonbetween the DLs of uniform stimuli, such as those in Klatt'sstudy, and DLs of changing timuli, as n the present tudy,can be made.

In any case, t seems easonable o assume hat, for sen-tence-level stimuli, the ease of Fo change udgments s in-

versely associated ith the amount (or steepness) f Fo per-turbation within the stimulus. Examination of Table IVshows hat this is true in most cases. One exception s thatMH and JW exhibit very similar DLs, though MH's Fo per-turbation s smaller han JW's. This may be explained y twofacts. First, JW is the slowest peaker nd MH is a rather astspeaker. Listeners may have had more time in judging JW'sreading han MH's. (If this assumption s true, DM's read-ing contains twofold difficulty--the Fo change s the lar-gest and the utterance s the shortest.) Second, MH's D Lsmay, in fact, have been smaller. His utterances were pro-cessed n 3-Hz steps and many of them received D Ls lessthan 3 Hz.

Results of Fo DL experiments or sentence timuli can-not be directly compared with those obtained rom experi-ments with simpler stimuli. However, t is nteresting o note

that some of our results--with the simplest stimuli (i.e.,three-word sentences) y some speakers whose Fo excursionwas relatively small--yielded DLs comparable with Klatt'sstudy, which used a synthetic vowel with steep Fo move-ments.

Little can be said about how inguistic nformation playsa role n DL judgments. For example, we assumed hat Fo ofstressed yllables, at the sentence evel, may have receivedmore attention by listeners han unimportant syllables. Butmore complex stimuli than those used n our experimentswill be required o test his assumption.

ACKNOWLEDGMENT

This work was carried out at Bell Laboratories, MurrayHill, NJ, with the assistance f Ann-Marie Quinn.

Atal, B. S., and Hanauer, S. L. (1971). "Speech nalysis nd synthesis ylinear prediction f the speech ave," J. Acoust. Soc. Am. 50, 637-655.

Flanagan, . L., and Saslow, . G. (1958). "Pitch discrimination or syn-thetic vowels," J. Acoust. Soc. Am. 30, 435-442.

Gold, B., and Rabiner, . R. (1969). "Parallel rocessing echniques orestimating pitch periods of speech n the time domain," J. Acoust. Soc.Am. 46, 442-448.

Harris, J. D. (1952). "Pitch discrimination," . Acoust. Soc. Am. 24, 750-755.

Klatt, D. H. (1973). "Discrimination f fundamental requency ontoursin synthetic peech: mplications or models of speech erception," .Acoust. Soc. Am. 53, 8-16. /

Malah, D. (1981). "Efficient spectral matching of the LPC residual sig-nal," Proc. IEEE ICASSP 3, 1288-1291.

Malah, D. (1982). "Cepstral esidual ocoder or improved quality trans-mission at 4-8 K bits," Proc. IEEE ICASSP 1, 622-625.

Mermelstein, P. (1978). "Difference imens or formant frequencies fsteady-state nd consonant-bound owels," . Acoust. Soc. Am. 63, 572-580.

Rosenblith, . A., and Stevens, . N. (1953). "On he DL for requency,"J. Acoust. Soc. Am. 25, 980-985.

't Hart, J. (1974). "Discriminability f the size of pitch movements nspeech," PO Ann. Prog. Rep. 9, 56-63.

't Hart, J. (1981). "Differential sensitivity o pitch distance, articularly nspeech," J. Acoust. Soc. Am. 69, 811-821.


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Difference Limens for f0