Figure 5.4 shows the means and standard deviations of duration in millisecond for Japanese vowels and consonants calculated from the word database. We can see that the standard deviations of the vowels are larger than those of the consonants, and that the variations of the consonant duration differ roughly in manner of articulation (refer to Table 5.1). Sagisaka et al (1992) showed that consonant duration is not affected as much as vowel duration by type of neighboring phonemes[39]. We focused on the vowel duration and examined its variation by replacing its preceding and following consonants with different ones.
