| Duration is one of the most important elements in the production of intonation,which plays a vital role in speech communication in daily life.The present study combines the speech synthesis method with the perceptionjudgment test and interviews to investigate whether the durational adjustment of vowels,pitch accents and inter-word junctures affect the speech naturalness or not. Thedurations of vowels in10single words, the durations of pitch accents and inter-wordjunctures in10multi-lexical-phrases have been modulated according to the durationalpatterns of the native speaker by using the software of Adobe Audition3.0.Through the comparison of durations between native and non-native speakers, thefollowing findings can be attained: Firstly, non-native speakers not only tend to confuseshort vowels with long vowels, but also produce the diphthongs with insufficientdurations. Besides, non-native speakers produce each syllable with prominence, andthey often confuse the accented syllables with unaccented syllables, which results in thefact that pitch accent durations of non-native speakers are rather shorter than those ofthe native speaker. Moreover, non-native speakers tend to produce redundant silences,self-repairs, or repetitions between words, which results in much longer durations ofinter-word junctures than the native speaker.Then the naturalness perception test was conducted, in which5evaluators listenedto the stimuli and rated them by using the9-point rating scale. After the perception test,the structured interview was conducted among the5evaluators to further explore theeffect of durational adjustment. The results of the naturalness perceptual test and theinterviews have unanimously shown:Firstly, durational adjustment of vowels can to some extent improve the speechnaturalness. The monophthongs of the non-native speakers become clear in the length,beneficial for differentiating between tense and lax vowels. The temporally adjusteddiphthongs enable the words pronounced with enough duration and gliding movement.Secondly, durational adjustment of pitch accents can improve the speechnaturalness to certain degree. Pitch accent adjustment makes the most stressed syllablesor words in phrases much more natural than the original versions because of thenative-like durations and sufficient prominence. Furthermore, after the durationaladjustment of pitch accents, the listeners can correctly catch the emphatic information ina phrase and major intentions or attitudes of the speakers, which is essential for speech communication.Thirdly, durational adjustment of inter-word junctures improves the speechnaturalness significantly. When the redundant silences, self-repairs, or pauses are cutout from the non-native speakers’ flow of speech, the junctures between words aretemporally tighter than before and the flow of speech become more coherent and fluent,leading to the obvious improvement in speech quality.Fourthly, among the three, the adjustment of inter-word junctures exerts thegreatest influence on speech naturalness, next is the vowel durational adjustment, whilethe durational adjustment of pitch accents makes the least influence on speechnaturalness.This study has highlighted several interesting aspects concerning the duration inspeech. It has alerted us to the serious deficiencies in the use of temporal factors in L2learners’ oral production, and that the modulation of those factors can significantlyimprove the quality of the speech. These findings have far-reaching implications for L2learning and teaching. |
