Vowels.
As regards vocalisation on one syllable, on long sustained notes and in the high register, the choice of vowels is a matter of some importance. The difference in the position of the mouth and lips in forming the open vowel a and the closed vowel ou is apparent to everyone. The series of vowels from the point of view of open sounds is: a, i, o, e, u. In women's voices the easiest vowel on high notes is a, for men it is o. The vowel i softens the penetrating quality of the top notes of a bass voice, and the vowel a adds to the extension of range in the very lowest compass. Lengthy florid passages are often written on the interjection ah, or simply on the vowel a. Owing to the restrictions imposed by literary and dramatic laws, the composer can only follow the above rules to a limited extent.
Examples:
Snegourotchka 293, 318-319 (cf. [Ex. 119]).
[No. 304.] Sadko 83.