Durational correlates of stress in Swedish, French and English*

Journal of Phonetics (1991) 19, 351-365

Durational correlates of stress in Swedish, French and English* Gunnar Fant, Anita Kruckenberg and Lennart Nord Department of Speech Communication and Music Acoustics, KTH, Box 70014, S-10044 Stockholm, Sweden Received 21st August 1990, and in revised form 5th December 1990

This is a pilot study on stress and timing organization in the reading of a 1 min long paragraph from a Swedish novel, translated into English and French. A common feature is the tendency of content words to receive stress, which accounts for interstress intervals of the same magnitude in the three languages. In French, minor stresses in nonterminallocations are manifested by intonation contours rather than by durational features . We have specifically studied the distribution of stress-induced duration increase within a stressed syllable. In nonterminallocations (i.e. excluding prepause locations), the emphasis is on the vowel and the preceding consonant in French, whereas in Swedish the lengthening is typically allocated to the vowel and the following consonants, and in English there is a more even balance in the lengthening of preceding and following consonants. In prepause locations the pattern of final lengthening is more similar in the three languages. Syllable durations have been related to syllable complexity and to degree of stress. The relative uniformity of syllable durations in French as a "syllable timed" language is related both to the predominance of CV units and to the lower degree of stress induced segmental lengthening. In Swedish and English the concept of "stress timing" is attributed not to a physical isochrony but to the relative auditory prominence of stresses. On the other hand, the similarities in interstress intervals of the three languages accounts for a rhythmical uniformity which is reflected in the timing of pauses.

1. Introduction In our earlier studies of Swedish prose reading and reading style (Fant & Kruckenberg, 1989; Fant, Kruckenberg & Nord, 1990), considerable attention was

devoted to acoustic correlates of stress and to the statistics of interstress intervals and how they integrate with pauses and other syntactic boundary markers. A study of the growth of interstress intervals with the number of phonemes or syllables, comparing Swedish, French , and English, was reported by Fant et al. (1989). Our present study has a more specific focus on durational patterns within the domain of a stressed syllable in these languages. How does stress affect vowel duration and the duration of consonants preceding and following the stressed vowel? To what extent 0095-4470/91/030351 + 15 $03 .00/0

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will language-particular patterns of syllable structure affect the overall duration of stressed and unstressed syllables? Can our results contribute somewhat to the perspective of "stress timing" vs. "syllable timing"? 2. Experimental procedure The main text from our Swedish studies (Fant & Kruckenberg, 1989), about 1 min of reading from a novel, was faithfully translated into French and English. These translations were read by native subjects, active in teaching. Table I provides an overview of text statistics, the number of stresses observed, and the overall speech rate. The present study is limited to one speaker for each language. We note that although the Swedish text contains a considerably smaller number of words than the French and English versions and although French leads in terms of number of syllables, the total number of phonemes in the three languages is about the same. The data on pause time and reading time probably reflect individual characteristics in the first place, but the faster speech rate for the French subject could be a characteristic of the language. Durations of phonemes, syllables and interstress intervals were obtained from spectrographic segmentations. For discussions on segmentation procedures and conventions see Carlson & Granstrom (1986), and Fant, Nord & Kruckenberg (1986) . In view of the varying terminology in French phonetics (see Touati, 1987), TABLE I. Basic data of translated texts Swedish Number of words Content words Function words Number of syllables Number of phonemes Number of stresses in content words in function words before a pause Total reading time (s) Total pause time (s) Average phoneme duration (ms) Unstressed vowels (ms) Unstressed consonants (ms) Average syllable duration (ms) Syllables per second Syllables per word Average number of phonemes/syllable* in stressed syllables* in unstressed syllables* Average duration of syllables stressed* prepause stressed unstressed* prepause unstressed * Prepause data excluded.

French

133 66 67 213 546 72 64 8 6 59 16.5 78 58 51 195 5.1 1.6 2.5 3.4 2.1

173 74 99 240 541

320 510 120 190

220 300 130

64

58 6 25 55 15.5 72.5 63 57 165 6.1 1.4 2.25 2.3 2.1

English

168 66 102 219 560 77 63 14 14 69 22 84 60 60 215 4.7 1.3 2.6 3.1 2.3 300 420 140 265

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the term stress might be questioned, but it is retained here as relative syllable prominence in all three languages. Stresses were assigned by listening, and the domain of a stress was then identified in the spectrogram with due consideration also to Fa contours . For Swedish, and on the whole also for English, this was a fairly straightforward task. In French it was more difficult. Besides the major stresses at the end of a phrase or a clause or a sentence or a specific semantic domain there are less obvious accentuations within a phrase. The realization of these often minor stresses was found to be quite different from those of major groups followed by pauses. A primary division of prepause vs. other locations was accordingly made to serve as a frame for the two accent types. In the prepause category we included cases of "virtual pauses" realized not by silence but by a short (about 100 ms) interval of incomplete cessation of the voice source with a local break into low Fa creaky voicing. In French, 25 out of 64 stresses were located in syllables next to a pause. In English the corresponding figure was 14 out of 77, and in Swedish only six out of 72. A majority of content words in each language was stressed, which accounts for the approximately equal number of stresses per language. 3. Interstress intervals

A direct consequence of the approximately equal number of stresses in the three languages is that the density of stresses and thus the average spacing between stresses become the same. We found quite similar values: 550 ms for Swedish, 565 ms for English, and 555 ms for French. These values pertain to what we call "free feet", which excludes intervals that span a pause or end with a pause, (Fant, Kruckenberg & Nord, 1989). In the analysis of Swedish and English we measured the foot from the onset of a stressed vowel to the onset of the next stressed vowel. In French, on the other hand, we defined the foot as ending with a stressed syllable,

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which conforms with the traditional accent pattern. This is what Wenk & Wioland (1982) refer to as "trailer timing", whereas the feet in Swedish and English are "leader timed". Figure 1 shows the results of linear regression analysis of the growth of free foot durations Tn with the number of component phonemes. For further details see Fant et a/. (1989). The trend is similar in the three languages. With reference to the straight line equation (1)

Tn =a+ bn

we find a larger offset value a in Swedish than in French or English, which is a feature that to some extent reduces the relative spread of foot durations. However, the language differences we observe in Figure 1 are not greater than what we may encounter for different speakers of the same language.

4. Segmental stress domains; relative phoneme durations The foot statistics apparently do not provide much language specific insight into stress patterns. We have to go inside the foot in order to study which segments have been affected by stress and how much. We shall look into segmental properties of phonemes and syllables and identify domains of stress-induced lengthening. We have quantified the lengthening by the difference between observed segment durations and an unstressed reference. These increments have been averaged separately for the stressed vowel and for the preceding and following consonants. The unstressed reference has been derived in two different ways, an unweighted value which is the average of all unstressed vowels or all unstressed consonants and a weighted value defined as the duration of the particular phoneme, averaged over all unstressed positions, prepause locations excluded. These have been labelled C_ 2 , C_t. V, Ct. C2 . Because of the relatively small corpus these values, especially C2 of French, should be regarded as indicative of trends only and limited to the specific speaker. (a) 80 60 II\

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However, the trends we have observed appear to be of general interest. The French data are shown in Fig. 2. The prepause durational increase at the upper half of the figure is systematically different from that of other stress locations shown in the lower part of the figure. The lengthening is much more pronounced in the prepause than in other locations, and this is especially true of the postvocalic consonant which is affected in prepause locations only. In other positions the stress-induced increase is limited to the vowel and the preceding consonants. In Swedish there is a quantity distinction between short and long vowels in stressed syllables, which is combined with a compensatory consonant duration . A consonant is short after a long vowel and long after a short vowel or the short vowel is followed by a consonant cluster. A similar tendency also occurs in English as illustrated in Fig. 3. In order to make possible a comparison of the three languages we have to exclude the prepause data, which eliminates the major stresses of French but allows a comparison under identical contextual conditions. As seen in Fig. 4, the stressinduced segmental lengthening in French is smaller than that of the two other languages and is on the order of 25 ms per phoneme or 50 ms per syllable and thus of low perceptual salience. Furthermore, we may note the dominance of the vowel and of consonants following the vowel in Swedish, whereas the English data show a more symmetrical distribution and the French increment profile excludes any effect on consonants after the vowel.

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5. Syllable types and syllable durations The duration of a syllable depends, on the one hand, on its complexity and specific phonological composition and, on the other hand, on stress and overall tempo and position within a phrase or a stress group. When comparing languages it is important to keep these factors apart. Our conventions for segmentation of the text into syllables have been language specific. Thus we have attempted to follow established norms for "liaison" in French (i.e. the left to right transfer of the last consonant of a word to initiate a syllable continuing with the vowel initiating the following word) . The English text has been segmented more or less conventionally. For Swedish we have adopted a morphological basis which on a few occasions secures consonants at the end of a root morpheme as a part of the stress domain. This is also needed in order not to place a syllablic boundary within a stressed VC unit. Because of the compensatory relation between the V and the C (i .e. V:C and VC:), it seems natural to let them belong to the same syllable. A consequence is that the average number of phonemes per stressed syllable in our Swedish data comes out somewhat larger than with a conventional syllable definition, 3.4 compared to 3.0, while unstressed syllables average 2.1, compared to 2.3 for the conventional definition. The corresponding figures for average durations are 320 ms vs. 290 ms for stressed syllables, and 120 ms vs. 125 ms for unstressed syllables. We shall next study the average growth of unstressed syllable durations with the number of phonemes they contain. As seen in Fig. 5 for Swedish, there is a quite linear growth of 50 ms per added phoneme plus a constant term of 10 ms. The French and English data are similar for one- and two-phoneme syllables but show somewhat higher values for three-phoneme syllables. The four-phoneme data points are less reliable but tend to be somewhat higher in English. Figure 6 provides a similar comparison for stressed syllables. In positions other than before a pause, i.e . in nonterminal locations, the durations for French are lower than for Swedish and English and increase at a slower rate, comparable to that of unstressed syllables. Prepause syllables tend to be shorter in French than in English. The Swedish data points were too few to be included in Fig. 6 but the average value is greater than for English (see Table I). It can be seen from Fig. 6

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that prepause syllables in French, which carry the main stresses, are of longer duration than English and Swedish syllables in other than prepause locations. The distribution of syllables with respect to the number of phonemes they contain is shown in Fig. 7. The most apparent feature here is the dominance of two-phoneme, mainly CV syllables in French. In English and Swedish unstressed syllables the two-phoneme category is also the most frequent but to a lesser extent. The two-phoneme category is also the most common in French stressed syllables. The average is 2.3 phonemes/syllable for French, 3.1 for English and 3.4 for Swedish stressed syllables. We may conclude that the smaller stressed/unstressed contrast of syllable duration in French, prepause data excluded, is the consequence of both a relatively smaller difference in syllable complexity and a lower degree of stress-induced segmental lengthening. These two factors are of approximately equal importance. 500.--------------------------------------. GJ

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ENGLISH , AC t1 = I syll able dura t io n

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Figure 9. Syllable durations minus unstressed reference values (weighted) in Swedish , French and English . Sentence 7 of standard text.

The net result is shown in Fig. 8. The ratio of stressed to unstressed syllable duration is 1.7 for French , 2.2 for English, and 2.7 for Swedish . Instead of average data we shall now study specific data on stress-induced syllable lengthening in sentence 7 of our standard text. The results for the three languages are shown in Fig. 9. The ordinate is the difference between the measured total duration of a syllable and the sum of the reference durations of all of its component

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phonemes (with each reference duration derived, as stated above, by averaging over occurrences of that particular phoneme in all unstressed contexts). The sentence contains four noun phrases of enumerative character followed by a verb phrase of explanatory nature. The English version was: "All this, the yellow light from the oil lanterns, the straw that rustled when they turned round, the musty smells in the crowded room, was something that she could perhaps get an impression of". The French translation: "Tout cela, la lumiere jaune des lanternes a petrole, la paille qui bruissait quand ils se retournaient, et les mauvaises odeurs qui flottaient dans la chambre bondee, elle pourrait peut-etre s'en faire une idee". The Swedish original: "Allt detta, fotogenlyktornas gula /jus, halmen som prasslade nar dom viinde sig och de onda lukterna i triingseln, kunde hon kanske bilda sig ett begrepp om". Our initially transcribed stresses have been marked in italics. There were 16 in the English version, of which three were prepause. The French version had 12 stresses , of which five were prepause, and the Swedish 14 stresses, of which only one was prepause. We may note the basic tendency of word initial location of stresses in English and Swedish versus the word final location in French. The immediate impression of Fig. 9 is the relatively low degree of stress-induced lengthening in French, of the order of 50 ms per syllable, which is two to three times smaller than in English and Swedish. There is a definite prepause lengthening affecting unstressed as well as stressed syllables in all three languages. There is no consistent phrase initial shortening of unstressed syllables within the sentence, at least not for French. Unstressed syllables immediately following a stress in French tend to be shortened. Occasionally, a phonologically unstressed syllable is lengthened as the last syllable of the word musty and the first syllable of the word flottaient, which could be considered as an instance of "accent d'insistance", also seen in the first syllable of cela. Also the noun lumiere is somewhat lengthened, indicating the conceptual tie to the following adjective jaune. Another observation is the increased tempo of the final verb phrase which is similar in all three languages, as is manifested by the lower than average duration of unstressed syllables and the very low level of durational increase of some stressed syllables in this final phrase, e.g. in the words something, peut-etre and bilda. 6. General discussion: stress timing vs. syllable timing This report has been concerned with durational correlates of stress only. Another limitation is that of the relatively small text corpus, about 1 min of reading by only one speaker for each language. Nevertheless some general tendencies of durational patterning emerge. Swedish and English are comparable in the sense that a stressed syllable attains a stress-induced lengthening of the order of 100-150 ms in positions other than before a pause, while in French the syllable lengthening is of the order of 50 ms only. These data verify our interpretation of the offset constant a of the foot duration regression line (Eqn (1)) in Fig. 1 as pertaining to an average degree of stressed syllable lengthening. For Swedish we noted a = 158 ms, for English a = 117 ms, and for French a = 106 ms. The latter value pertains to "trailer timed" feet. However, with the alternative definition of the foot as "leader" timed as in Swedish and English we noted a = 77 ms (Fant et a/., 1989). The identification

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cannot be expected to be perfect since secondary zones of stress in a foot may interfere as discussed above. In French there is a clear dominance of prepause stresses. Here the lengthening is greater than in non-prepause contexts of Swedish and English (see Fig. 6). The largest prepause lengthening was found in Swedish, followed by English (see Table I). However, these data are limited by the small corpus size and could be speaker specific. It seems logical to decompose the durational measures of prepause stresses into two additive components, one related to stress alone and the other to the final position. The prepause component induces a lengthening of phonemic segments, which on the whole is inversely related to the distance between the segment and the pause boundary. Stresses in other positions behave differently in the three languages. In Swedish the lengthening influence is skewed to the right, favouring consonants after the stressed vowel, whereas in French the profile is skewed to the left, with no influence on consonants after the stressed vowel. This finding is coherent with the relevance of VC units in Swedish and of CV units in French. In English the influence is more symmetrically balanced. An addition of a separate prepause lengthening will explain a major part of the durational pattern of terminal stresses in all three languages. Duration is but one of the relevant stress parameters. The intonation pattern and specifically the local F 0 modulations are equally important and in French dominating. A substantial part of the minor stresses we noted here did not convey any significant durational cues, but all of them displayed a definite F 0 contour, generally with a continuation tone pattern of a slow rise towards the nucleus of the stressed syllable followed by a resetting of F 0 at a faster rate towards the initiation of the next foot. In our study we have as yet not documented F0 data from these minor stresses nor from the more apparent terminal, prepause contours. For a description of basic prototypes see e.g. Delattre (1965, 1969). A related project is that of Touati (1987, 1989) comparing tonal configurations of text reading in French and Swedish; see also Garding (1981) . We shall not attempt a detailed comparison of our data with previously published data. Not much has been published from data bank material of a similar kind. We may note a qualitative agreement with data of Delattre (1965, 1966) and Crompton (1980) for French. Our data on average durations of stressed and unstressed syllables in English, 300 ms and 140 ms, happen to coincide closely with comparable data from Campbell (1989), 294 ms and 138 ms respectively. There also remains the need to study intensity as an additional stress parameter. We share the common opinion that intensity is of less importance than duration and F0 • According to the data of Delattre (1966) intensity is insignificant for word stress in French but could be of some importance in English. In order to facilitate vowel specific normalization we suggest that one should measure equivalent voice source parameters (Fant, 1980; 1988). However, one difficulty is the covariation of stress and articulation, which in Swedish causes a deemphasis of the intensity of stressed maximally close long vowels /i:/, /y:/, /tt:/ and /tt:/, these being perturbed towards a homorganic fricative. Another aspect of stress-articulation interaction that we have noted in Swedish is the loss of segmental contrast between a voiced occlusive and surrounding vowels under conditions of deemphasis (Fant et al., 1986; Fant, 1987). It is well known (see e.g. Delattre, 1969a) that an absence or a smaller degree of

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vowel reduction is typical of French. As an example from our follow-up of these studies we may note that we found exactly the same average F 1 =400Hz, F 2 =1910Hz and F 3 =2630Hz of the vowel /e/ in French stressed and unstressed positions. "Stress timing" vs. "syllable timing" are concepts frequently used in language descriptions. The stringency and relevance of these terms, originally coined by Pike (1946) and promoted by Abercrombie (1967), have often been questioned (see e.g. Adams, 1979; Wenk & Wioland, 1982; Dauer, 1983; Scott, Isard & de BoyssonBardies; 1985; den Os, 1988; Fletcher, 1991). What evidence is there for referring to Swedish and English as stress timed and to French as being syllable timed? The initial postulate was that of a regularity of interstress intervals in stress-timed languages and a regularity of syllable intervals in syllable-timed languages. Our data support the findings of Dauer (1983) that irrespective of language type the interstress intervals within one and the same sentence may cover a range of about 0.2 to 1 s. We find a typical mean value on the order of 550 ms in free feet, i.e . disregarding feet that span a pause or include a prepause lengthening. The duration of a foot grows with the number of phonemes included at the same rate in all three languages (see Fig. 1). Absolute isochrony does not exist except in metronomical reading. The increment of foot length per added phoneme segment (the constant b of Eqn (1)) is of the order of 50-60 ms, which is close to the &verage duration of unstressed phonemes. As could be expected, the same increment per added phoneme also recurs in the growth of unstressed syllable duration with the number of phonemes contained (Fig. 5). The higher speech rate of French is thus mainly a matter of the lower degree of stress-induced lengthening in non-terminal locations. Foot length compensations for added number of segments are small. Available data from the literature generally derive from constructed laboratory sentences . Measured durations may accordingly be affected by the total utterance length and thus may not be representative of connected text reading . For Swedish , Strangert (1985) reports a shortening of a stressed syllable, mainly occurring with the addition of a first subsequent unstressed syllable. Duez & Nishinuma (1985) did not find a compression effect for French but noted a rhythmical alternation of unstressed syllables. In both the Swedish and English texts of the present study we have noted a shortening of the stressed syllable of the order of 10 ms per added unstressed syllable up to the third. However, this corpus is too small to ensure statistical significance. For an English data base Campbell (1988) reports foot level shortenings on the order of 50 ms for th.e first added unstressed syllable and 20-30 ms for additional unstressed syllables. Still these effects are not large enough to cause saturation effects and their perceptual relevance may be questioned. As proposed by Allen (1975) and Lehiste (1977) , the spread of interstress intervals is averaged out in perception. This is a reasonable assumption which gains support from our findings (Fant & Kruckenberg, 1989; Fant, Kruckenberg & Nord, 1990), that a rhythmically sensitive reader tends to plan pauses plus associated prepause lengthening to coincide with a multiple integer of the short time average value of free foot durations. Such trends were earlier reported by Lea (1980), and we have found them in all three languages (Fant et al. 1989). Stress rhythm is thus enhanced by pausing. Some aspect of stress timing would thus also prevail in French. The situation is actually more complex. Let us approach the rhythmical aspects

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from a broader perspective . We have to consider temporal regularities on at least three, perceptually competing, simultaneous and superimposed levels: a syllabic level , a stress foot level , and a major phrase boundary level. There is also a rhythmic aspect of tempo changes inherent in the speeding up and slowing down according to the demands of the semantic contents. The latter higher order groups are found in all languages . The density of stresses is also language universal, reflecting the equal proportion of content and function words. In French the non-terminal stresses are less apparent. Instead , as we have shown , the syllabic rhythm attains a perceptual prominence, being more regular and less masked by word stresses. In addition , the terminal, prepause stresses marked by apparent durational and F0 cues are a dominating feature of French prosody, which may attain a rhythmical quality. According to Martin (1987) there is evidence for prosodic marking of words within a sentence or clause in French to conform not only with syntactic but also with rhythmic demands to avoid uneven distributions of stress. In English and Swedish the stresses are not regularly spaced, but they attract the listeners' attention. The timing of stresses and their rhythmic impact follow certain rules that are as yet not fully investigated. The remark of Allen (1975, p. 80) , that " stress rhythms are thus rhythms of alternation , whereas syllable rhythms are rhythms of succession" , is of certain relevance. The interstress interval appears to be a potential domain for compensatory adjustments. In a study of durational rules for synthesis, Carlson, Granstrom & Klatt (1979) found a correct timing of stressed vowel onsets to be perceptually important. On the other hand , apart from foot level compensations, a correct timing of interstress intervals is automatically preserved if segmental durations within the foot have been realistically predicted. Higher order compensation effects should also be considered. One such effect that we have found in Swedish is the tendency of a net balance between larger and smaller degrees of stress within a sentence and thus of foot lengthening and shortening (Fant & Kruckenberg, 1989), supporting earlier statements of an economy principle (e.g. Ohman, 1967; Garding, 1991). A final conclusion is that a study of foot (i.e. interstress interval) statistics is not sufficient as a basis for describing major language differences , e.g. to express the manifestation of stress timing vs. syllable timing. The language specific features are found inside the foot. This study has largely been concerned with durational patterns . Contrasts in stressed and unstressed syllable durations should be considered with due regard to both the relative complexity of syllables, in terms of number of phonemes per syllable, and stress-induced lengthening effects. Both factors contribute to the relative heaviness of non-terminal stressed syllables in Swedish and in English and thus to a greater stressed/unstressed contrast than in French. Unstressed syllables are of about the same duration in all three languages. Vowel reduction adds to the contrast in English and Swedish. In French the resistance to articulatory reductions reduces the stressed/unstressed contrast. Furthermore, the relatively low impact of non-terminal stresses in French is associated with smaller F0 modulations than in the major, usually prepause stresses. These are in our view the main arguments for referring to French as syllable timed and Swedish and English as stressed timed. Stress timing is not a matter of physical isochrony of interstress intervals but a perceptual dominance of heavy syllables, the succession of which is sensed as quasiperiodical. A language is sensed as syllable timed when the differences between stressed and unstressed syllables are reduced.

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This involves both a reduction of stress cues and a relatively greater precision and uniformity of unstressed syllables. This has been a pilot study. Other language specific features reside in intonation patterns, voice source dynamics and articulatory patterning. We intend to continue research along these lines and collect data from more speakers and within a larger corpus. This study has been supported by grants from The Bank of Sweden Tercentenary Foundation, The Swedish Council for Research in the Humanities and Social Sciences and The Swedish Board for Technical Development. We are indebted to Danielle Duez for comments on our stress notations of the French text and to Paul Touati and Jacqueline Vaissiere for comments on our manuscript.

References Abercrombie, D. (1967) Elements of general phonetics. Edinburgh University Press. Adams, C. (1979) English speech rhythm and the foreign learner, Janua Linguarum Series Practica, 69, Mouton. . Allen, G. D . (1975) Speech rhythm: its relation to performance universals and articulation timing, Journal of Phonetics, 3, 75-86. Campbell, W. N. (1988) Foot-level shortening in the spoken English corpus. In Proceedings of FASE 88, Edinburgh, pp. 489-494 . Campbell, W. N. (1989) Syllable duration determination. In Eurospeech 89, Vol. 2, pp. 698-701. Carlson, R. & Granstrom, B. (1986) A search for durational rules in a real-speech data base, Phonetica, 43, 140-154. Carlson, R., Granstrom, B. & Klatt, D. (1979) Some notes on theperception of temporal patterns. In Frontiers of speech communication research (B . Lindblom & S. Ohman, editors), pp. 233-244, Academic Press . Crompton, A. (1980) Timing patterns in French, Phonetica, 37,205-234. Dauer, R. M. (1983) Stress-timing and syllable-timing reanalyzed, Journal of Phonetics, 11, 51-62. Delattre, P. (1965) Comparing the phonetic features of English, French, German and Spanish: an interim report. Heidelberg: Julius Groos Verlag. Delattre, P. (1966) A comparison of syllable length conditioning among languages, International Review of Applied Linguistics (IRAL), 4, 183-198. Delattre, P. (1969a) An acoustic and articulatory study of vowel reduction in four languages, International Review of Applied Linguistics (IRAL), 7, 295-325 . Delattre, P. (1969b) The general phonetic characteristics of languages. Final report OEC-0-9-0977010775/014, US Dept. of Health, Education and Welfare. University of California, Santa Barbara, 1969. Duez, D. & Nishinuma, T. G. (1985) Some evidence on rhythmic patterns of spoken French. Dept of Linguistics, University of Stockholm, PERILUS IV, pp. 30-40. Fant, G. (1980) Voice source dynamics, STL-QPSR, Nos 2-3, 17-37. Fant, G. (1987) Interactive phenomena in speech production. In Proceedings of XIth international congress of phonetic sciences (ICPhS), Tallinn, USSR, Vol. 3, 376-381. Fant, G. & Kruckenberg, A . (1989) Preliminaries to the study of Swedish prose reading and reading style, STL-QPSR , No. 2, 1-83. Fant, G., Kruckenberg, A. & Nord, L. (1989) Rhythmical structures in text reading. A language contrasting study. In Eurospeech 89, Vol. 1, pp. 498-501. Fant, G., Kruckenberg, A. & Nord, L. (1990) Acoustic correlates of rhythmical structures in text reading. Nordic Prosody V, pp 70-86, Painosalama Oy, Turku. Fant, G . , Nord, L. & Kruckenberg, A. (1986) Individual variations in text reading. A data-bank pilot study, STL-QPSR, No.4, 1-17. Fletcher, J. (1991) Rhythm and final lengthening in French. Journal of Phonetics, 19, 193-212. Gobi, C. (1988) Voice source dynamics in connected speech, STL-QPSR, No. 1, 123-159. Garding, E. (1981) Contrastive prosody: A model and its application, Studia linguistica, 35(1-2), 146-165. Garding, E. (1991) Intonation in Swedish. To be published in Intonation Systems (A. di Cristo & D . Hearst, editors), Cambridge University Press (forthcoming) . Lea, W. A. (1980) Trends in speech recognition. Prentice Hall. Lehiste, I. (1977) Isochrony reconsidered, Journal of phonetics, 5, 253-263. Martin, P. (1987) Prosodic and rhythmic structures in French, Linguistics, 25, 925-949 . Os, E . den (1988) Rhythm and tempo of Dutch and Italian. Elinkwijk BV, Utrecht.

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Ohman, S. (1967) Word and sentence intonation : A quantitative model , STL-QPSR Nos 2-3, 20-54. Pike, K. (1946) Intonation of American English. Ann Arbor, MI: University of Michigan Press. Scott, R ., Isard , S.D. & de Boysson-Bardies, B. (1985) Perceptual isochrony in English and in French, Journal of Phonetics, 13, 155-162. Strangert, E . (1985) Swedish speech rhythm in a cross-language perspective. Stockholm: Almqvist & Wiksell International. Touati, P. (1987) Structures prosodiques du suedois et du fran~ais . In Travaux de l'institut de linguistique de Lund. Lund University Press. Touati , P. (1989) French and Swedish tonal configurations in read text, STL-QPSR, No . 1, 33-36. Wenk, B. J. & Wioland, F. (1982) Is French really syllable timed? Journal of Phonetics, 10, 193-216. STL-QPSR is an abbreviation of Speech Transmission Laboratory Quarterly Progress and Status Report, Department of Speech Communication and Music Acoustics, Royal Institute of Technology (KTH), Stockholm .