[espeak-ng:master] New Comment on Pull Request #810 Add some patterns to ja_rules
Using separate vowels would mean that ああ would be pronounced differently to あぁ and あー, as
/aa/ would have a slight pause compared to
A possible solution would be to define a group for each long vowel set (a, e, i, o, u), e.g.:
.L22 ぁ ー // long a
then have a new rule such as:
あ a // a
あ (あL22 a // aā
ああ a: // ā
あぁ a: // ā
あー a: // ā
aā rule is a new rule to fix the case you describe. This would need to be done for each of the doubling rules.
This means that
ああー will be pronounced as
/aa:/. These rules cannot currently be simplified due to limitations in the espeak/espeak-ng rule processing logic. I'll raise a separate issue for that.