The English phonetic system includes 10 vowels of the 11 monophthongs or pure vowels of the English Language, missing the phoneme /ɑː/ or open unrounded vowel.
The pronunciation of some vowels may change slightly, depending on the dialect or the way the Vocaloid was recorded.
Also the target or optimal musical genre of the Vocaloid can affect the pronunciation of the vowels:
- Example: Tonio & Prima had been reported to have an "opera" like pronunciation of the vowels, more fitting for romance languages than standard English. This probably is attributed as they're Opera specialized voicebanks.