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41

VOWEL CONTRAST REDUCTION IN TERMS OF ACOUSTIC SYSTEM CONTRAST

IN VARIOUS LANGUAGES *

Tjeerd de Graaf**

and Florien J. Koopmans-van Beinum

1 . INTRODUCTION

The aim of this paper is to demonstrate that the measure for Acous-·

tic System Contrast ASC (Koopmans-van Beinum, 1980) can be used not

only for description and comparison of vowel contrast reduction in

various speech conditions of one language, but also to compare the

degree of vowel contrast reduction in various languages, whether these languages involve many vowels in their vowel systeir. or only a few. We might hypothesize that systems involving fewer vowels

wo�ld display more contrast reduction than richer vowel systems

since the acoustic vowel space is less filled. Next we want to show that the ASC measure can also be used to com-

pare the degree of contrast between the set of long vowels and the set of short vowels in those systems that contain quantitatively

paired voweln.

Finally some problems will be discussed with regard to the descrip­

tion of vowel contrast reduction in languages involving a substan­

tial number of nasal vowel s in their vowel system.

2. COMPARISON OF VOWEL SYSTEMS

Several studies on systematics in the distribution of vowels within

* This is an extended version of a paper read at the lOth Interna­tional Congress of Phonetic Sciences, Utrecht, August 1983.

** Iy·�titute of Phonetic Sciences, Groningen University •

I

43

monly reported difference of quality between long and short vowels

of corresponding position is centralization of the short vowels

(Lehiste, 1970, pp. 30-33). If so, then the resulting ASC values

for the short vowel subsystems must be smaller than for the corre­

sponding long vowel subsystems.

For vowel systems containing nasal vowels the following universal

property holds: the number of nasal vowels in such a .v:owel syst;em

is equal to or sma l ler .than the number of oral.vowels (Ruhlen,

1975). In his sample Crothers (1978) has 50 languages (24%) with

nasal vowels. In our study we take Polish (6 oral vowels and 2

nasal vowels) and French (12 oral vowels and 4 nasal vowels) as representative examples. Only the oral· vowels are included in this

study. Fig. I displays the various vowel systems as used in this study. The vowels are represented in stylized diagrams according to the

articulatory dimensions high-low and back-front, in the sar:e way as

used for the first time by Hellwag (l 78i). For Polish and French

the nasal vowels are indicated separately, whereas for Hungarian

and Frisian we give the short and corresponding long vowels also

in a parallel way.

3. SPEECH NATERIAL AND MEASUREMENTS

The speech material in this study consisted of vowels spoken in

isolation, vowels from isolated words, and vowels from a context.

In most cases free conversation is used for this context whereas

some rare vowels in a many-vowel system are se.lected from sen-� '. .

tences read- from a�specific text. For each vowel in each of the

speech conditi�ns the formant values Ft and F2 are determined as

the average over a number of tokens from the speech material. Since

the distinction between stressed and unstressed syllables is not

equall y clear in <iil languages� we did not involve that di.stin.c­tion in our speech material apart from the fact that totally un­

stressed syllables have been omitted . For the Dutch data � which

were the result of earlier measurements (Koopmans-van Beinum, 1980)

42

the vowel systems have demonstrated or confirmed that the natural

languages of the world for the greater part display an acoustical­

ly and perceptually highly balanced dispersion of vowels in their

vowel system (Liljencrants and Lindblom, 1972; Disner, 1980;

Koopmans-van Beinum, !983).

In order to attain our object as given in the Introduction we ex­

amined languages involving few vowels in their vowel system (Japa­

nese, Polish), many vowels in their vowel system (Dutch, French,

Hungarian, Frisian), languages with quantitatively paired vowels in

their system (Hungarian, Frisian), and languages involving nasal

vowels (Polish, French) of which only the oral vowels are used here.

In a survey of vowel systems Crothers (1978) indicates that nearly

half of his 209 sample languages have contrasting long and short

vowels. In most cases (70%) the vowels of the two systems are equal

in number and arrangement. Two languages in our investigation

(Hungarian and Frisian) can be considered as representative examples

(in the case.of Hungarian the two vowels [a:] and[:,] are taken as a

pair, although their qualities differ considerably). The most corn-

Japanese u Fig. a e l. Vowel systems for

a the languages used in this study.

Polish u � 0 e 0 e

a

Dutch u y o: - �: e:l

j ce E u a:

French u y 0 Ii.a e

j oe " 5 re E et a a

Hungarian u y u: y: l: 0 !/> e o: �: ...

:I a:

Frisian u y LI! Y: l: 0 al'! 1 o: v\: e:

:) " :>: E: Cl a:

F

44

we averaged the vowel data of the stressed and the unstressed syl­

lables from free conversation.

For the Dutch material and for part of the French speech material

formant frequencies (F1 and F2) were measured by spectral analysis

(Wempe, 1979). For the other languages formant frequencies were

measured by LPC analysis. In both methods a more or less stable

central ·se'gment of the vowel was determined as being characteris­

tic for 'the whole vowel part, and used for measurement.

Figs. 2 td 7 display �he mean FI - F2 position per vowel per speech

condition, given in a logarithmic Fl - F2 vowel chart, for one

speaker per language. The C-symbol indicates the speaker centroid,

being the overall mean of the measured log Fl and log F2 values

per speaker (the average value is calculated over all non-nasal

vowels and all speech conditions).

F2 ___ _

600 I 800 1000 1200 I I t l ! 1 ! I

300 I ( �;o �

• .---. \ 500 I G O:o�, 800 '

900

Iii VOWELS IN ISOLATION

V VOWELS IN WORDS

F1

F2 ___ _

600 800 1000 1200

300 Hz ' u

' I ! ! !

400 I ..____, I '8 500 f-600 � 0�

700�! 800 �

900 "-'

1000

c

16,00 2000

...

l ( \ e

! I

!I VOWELS IN ISOLATION

V VOWELS IN WORDS

3000 Hz

/''°' VOWELS If\! FREE CONVERSATION e VOWELS IN FREE CONVERSATION

Fig. 2. Mean formant frequencies per Fig. 3. Mean formant frequencies per vowel per speech condition (connected per vowel) in

Polish (speaker P2).

vowel per speech condition (connected pervowel) in Japanese (speaker Jl). C indicates the �peaker centroid.

I I ­I I

F2 __ _ sf 600 1000 1200 16.00 2900 30,00 Hz II I.' ! I I 1--t-r I lJ1 l 'l

300 r � JJ ::: [_ u� �Bx � 600 \ \. � � � Q.�\'V.... �

Ill VOWELS IN ISOLATION � VOWELS IN WORDS � VOWELS IN FREE CONVERSATION

Fig. 4, Mean formant frequencies per vowel per speech condition (connected per vowel) in Dutch (speaker DJ).

F2 __ _

I'll VOWELS iN ISOLATION v VOWELS IN WORDS

@I VOWELS IN FREE CONVERSATION

Fig. 6. Mean £ormant frequencies per vowel per speech condition (connected per vowel) in

Hungarian (speaker Hl).

F

Ill VOWELS IN ISOLATION "' VOWELS IN WORDS

3000 Hz ' 1' I � �

G VOWELS !N FREE CONVER!::AT!ON

Fig. 5. Mean formant frequencies per vowel per speech condition· (connected per vowel) in French (speaker F2).

F2 ___ _

soo eoo 1000 1200 h--;;l---r ! I I I ; � i u"'"-."'f.... 300 � · -� Hz i

1600 2000 3000 Hz II ly.I '·']I

I ' ·I. 1•·1 1' �"/ ·�71 \ � "{ ff I \'f, JJ._f ! I

���� ·:t �e: ii

� ar:f; Jr; ti a c.,. 11 7 0� � .. /�

800 'X1 Cl . ,/ 900 � "'

"-t � I � Iii t: I I : I ·I li e--!

1000 ' '1 '*--t---+---+--ii--i--t-+-H� 1200

II! VOWELS JN iSOLAT!ON

� VO'NELS IN WORDS ® VOWELS IN FREE CONVERSATION

Fig. 7. Mean formant frequencies per vowel per speech condition (connected per vowel) in Frisian (speaker Fnl).

46

4 . ACOUSTIC SYSTEM CONTRAST

In accordance with the convention used by Koopmans-van Beinum (1980) all formant values were transferred to the logarithmic expressions

LF. 100.101og F. l_ 1.

with i = l or 2.

From these values the Acoustic System Contrast (ASC) was calculated

which is equal to the mean square of the distances in the Fl - F2

plane between the different formant values for the vowels and the

centroid according to the formula

N j " rv. -+) 2 ASC = N .6 \ 1 - c

3=l .J

in which V. is the two-dimensional vector for the vowel J in the J

FI - F2 plane and � is the vector for the centroid C.

In this way we acquired the dispersion or total variance of the

ASC

200

100

� I 1 I' I

n

0 IW.et!on B .,_d,. � CC-nllf:fS3tlon

J1 12 Ja P1 P2 01 02 03 04 F1 F2 Ht H2 Fn1 Fn2

Fig. 8. Histogram illustrating the vowel contrast reduction for three Japanese speakers (Jl, J2, J3), two Polish speakers (PI, P2), four Dutch speakers (DI, D2, D3, D4), two French

speakers (F l, F2), two Hungarian speakers (H 1, H2) and two Frisian speakers (Fnl, Fn2).

47

whole vowei system in each of the speech conditions, or the disper­

sion of subsets of the vowel system, e.g. long vowels versus short

vowels, expressed in values comparable among themselves.

Table 1 gives the ASC values for each of the speakers and speech

conditions used in this study, whereas in Fig. 8 the same data have

been displayed in a histogram.

Table l. ASC values in various languages

T Language I Speaker Vowels in Vowels in Vowels in

nr. isolation l words conversation

.

Japanese l 613 I 383 206 2 I 50i 363 254

3 540 322 i49 • i

Poiish I I 744 I 311 273

2 608 405 I 214 I

Dutch 426 418 272

2 400 310 178 3 447 374 197 4 634 529 319

French 692 442 272

2 463 306 157

Hungarian 675 515 341

2 720 484 375

Frisian 621 408 317

2 624 518 256

•

600

I F1

'ol Hz 400

' 500 600

F2

800 10001200 ! , I !°"11 I

•, 'e.

o: / \ Iii

1500 :woo 3000 Hz i I I

I I 'i I ' :y;! : I i i � ' ' ii· ;I: �1:JJ

� ./"'- ' ! ll ' !J • ! i I e. i I c I "

e -H ! I i

I I , : i -+-H " .21:

i I ! j ' .+m. I I ! : I

m VOWELS IN ISOLATION '*' VOWELS !I'll WORDS tll VOWELS IN FREE CONVERSATION

Fig. 9. Mean formant frequencies per vowel per speech condition (connected per vowel) in

Hungarian (long vowels, speaker H2).

600

300 Hz I 400 I

500 500

F2 ___ _

800 10,00 1?00 I i

e:

rnoo 2000 3000 Hz I I l I Y:i I i:i ! I

ITT ' I�: i I <) +1 l I �e; j i

�,(!: +i c t) i i I! +-! I . _;1: � I I

tt1 � 1000 �

1 I i+H-1 12 o o *-�-r-1 --+--1-t1-+--+1 �1-+-! .L..ji I

fill VOWELS IN ISOLATION

T VOWELS IN WORDS 9 VOWELS IN FREE CONVERSATION

Fig. 11. Mean formant frequencies per vowel per speech condition (connected per vowel) in Frisian (long vowels, speaker Fn 1 ) .

48

600 I I

F1 JOO L I I Hz I I 400 ! I

500 [ t !

600

F2 ___ _

aoo 1000 1200 i ! i i ! I

1200

1600 2000 3000 Hz

.l)J!� 4c � I 1 �e 11 ii tH ;m ! '

I

!!! VO'NELS IN ISOLATION .., VOWELS IN WORDS ® VOWELS !N FREE CONVERSATION

Fig. J 0. Hean formant frequencies per vowel per speech condition (connected per vowel) in

Hungarian (short vowels, speaker H2).

F1

F2 ___ ,..

ra VOWELS !N ISOLATION v VOWELS IN WORDS tli VOWELS IN FREE CONVERSATION

Fig. 12. Mean formant frequencies per vowel per speech condition (connected per vowel) in Frisian (short vowels, speaker Fnl).

49

5. COMPARISON OF THE RESULTS IN VARIOUS LANGUAGES

As can be seen in the vowel diagrams (Fig. 2 to Fig. 7) all lan­

guages in this study display a centralizing shift if one goes from

vowels pronounced in isolation to vowels in conversation. The cal­

culated values of the acoustic system contrast ASC give the possi­

bility to compare the degree of reduction between the various

speech conditions and languages as well as between the various

speakers (Table and Fig, 8). Thi::re is no indication for a system-

atic difference between vowel systems with a small number of vowels

and those with a large number of vowels, as was hypothesized in the

Introduction. Although we did not yet perform any statistics on

these data, and the number of speakers per language is very low, it

seems to be justifiable to conclude that vowel contrast reduction

occurs as a universal property of all languages, the differences in

the amount of reduction being mainly speaker dependent. This suppo­

sition is reinforced by the fact that speaker 3 of Japanese, spe'.lk­er 2 of Dutch, and speaker 2 of French, are the very speakers with

the smallest ASC values in free conversation, and were judged by

their interviewers to be the speakers least careful in pronouncing.

Table 2 . ASC values for the subsystems of long and short vowels for two languages.

Languag8 Speaker\ . Vowels in Vowels in I Vowels in l I nr. isolation I words conversation

long short long short long short

I 428 255 Hungarian I 1 768 583 695 336 I

2 859 532 I 596 372 I 430 32i I f

Frisian l 680 562 460 355 354 280

2 655 593 563 l 473 289 223 J

I

ASC 800

n

H1

50

Fn 1

OJ lsolailon CTJ words � Conwt&lliion

Fig. 13. Histogram illustrating the vowel contrast reduction for two Hungarian and two Frisian speakers, where the ASC values are indicated separately for the long vowels (left) and the short vowels (right).

In the case of languages with equal numbers of long and short vowels

(Hungarian and Frisian) the vowel diagrams for the long and short

vowel s are given separately in Fig. 9 to Fig. 12, whereas the sepa­

rately calculated ASC values are given in Table 2 and in Fig. 13 in a histogram. Here we find for the long vowels in each speech situa-

tion a larger value of the ASC than for the short vowels, which il­

lustrates the fact that in general long vowels a.re more peripheral

than the corresponding short ones.

6 . VOWEL SYSTEMS WITH NASAL VOWELS

In our initial attempt to include in this study some languages in­

volving nasal vowels in their vowel system (cf. Polish and French),

we came across several problems, some of them of methodological

nature.

5!

In the first place part of the recorded nasal vowels turned out t o

yield very unreliable measurements, o r even measuring was impossi­

ble. This made our data on nasal vowels very incomplete.

If measuring was possible, a second problem arose in the applica­

tion of the ASC algorithm, because of the special, 'nasal1 low for­

mant frequency, beside Fl and F2 frequencies. Are we allowed to

leave these nasal formants out of consideration, and can the Fl and

F2 of nasal vowels be compared with those of oral vowels without

further ado? These two problems decided us to exclude the nasal vow­

els from the present study. But this decision caused another method­

ological problem: If indeed a vowel system is acoustically and per­

ceptually highly balanced, then the nasal vowels will make up an

essential part of this balance and therefore must not be excluded.

In the case of the Polish vowel system we believe the loss is not

too serious, since both nasalized vowels ( 0 and e ) are more or

less in balance in the vowel system. The problems for the French

vowel system are much more serious, since exclusion of the nasalized

F2 ___ _

eoo aoo 1000 1200 1600 2000 1---,---l-t -.-�;-,-�·�..,....--t-_JI I !.·

300 Hz 400 �

I i ' I

,. -s• I if ,..#� ' 500 -

600

70�1 SOO� 900 �· 1 000

• 1 I I ! 1200 · . I i '

1=: Gl VOWELS iN ISOLATION 2= � VOWELS IN WORDS

sooo Hz . , I i I i )� I, ! I I . I I �n I

3,. e VOWELS IN FREE CONVERSATION

Fig. 14. Shift of the centroid for two French speakers.

52

vowels ( 3, re, a and E ) might disturb the balance. Indeed, re­

sults concerning the French oral vowels display deviations from

the other results: whereas in all other cases the centroids per

speech condition stay stable, we can establish a clear shift of these

centroids into the direction of 'high front' for both French speak­

ers (Fig. 14). Nieboer (forthcoming) who performed the measurements

of the French speech material, suggests a phenomenon of 'anterior­

is�'. being the very French articulation base, instead of the cen­

tralizing reduction tendency in other languages when going from

vowels pronounced in isolation to vowels in free conversation.

However, which is the role of the nasal vowels in this respect? In

any case a role we had to leave out of this study but one that earns

more attention in future research on vowel systems.

. -

53

REFERENCES

Crothers, J. (1978). Typology and Universals of Vowel Systems.

Universals of Human Language. Vol. 2: Phonology.

Edited by J.H. Greenberg. Stanford University Press,

Stanford, California.

Disner, S.F. (1980). Insights in vowel spacing: results of a lan­

guage survey. UCLA Working Papers 50: 70-92.

Hellwag, C.F. (1781). Dissertatio inauguralis physiologico medica

de formatione loquelae. Tiibingen. Facsimile with a

translation in Dutch, Institute of Phonetic Sciences,

Arns terdam l 96 7.

Koopmans-van Beinum, F.J. (1980). Vowel Contrast Reduction: An a­

coustic a.rid perceptual study of Dutch vowels in

various speech conditions. Diss., University of

Amsterdam.

Koopmans-van Beinum, F.J. (1983). Systematics in vowel systems. In:

M.P.R. van den Broecke� V.J. van Reuven and W. Zonneveld

(Eds.), Sound structures: Studies for Antonie Cohen.

Faris Publications. Dordrecht, i59-171.

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Liljencrants, J. & Lindblom, B. ( J 972). Numerical Simulation of

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trast. Language 48, 839-862.

Nieboer, G.L.J. (forthcoming). Kl:i.nkercontrastreduktie in bet Frans.

To appear as IFA-report 77, Institute of Phonetic

Sciences, Amsterdam.

Ruhlen, M. (1975). A Guide to the Languages of the World. Language

Universals Project. Stanford University.

Wempe, A.G. (1979). An experimental segment spectrograph based on

some notes on frequency analysis of speech segments.

Proceedings of the Institute of Phonetic Sciences

Amsterdam 5, 44-102 .