Hello, my name is missike_39.
I have a hard time writing English, so please excuse the automatic translation.
Are you talking about how to make consonants? What I mean by this is that consonants are not continuous waveforms, so they cannot be synthesized by sine wave synthesis as before, so we need to create noises that resemble consonants somehow.
To be more specific, here is a site that shows frequency analysis of Japanese speech, etc. Based on this information, we can adjust the frequency components specific to consonants using an equalizer, etc., and create them one by one. This is a process that requires a lot of patience and a certain sense.
音声認識~周波数スペクトルで音素を判別
https://myonseininsiki.syogyoumujou.com/boin_aiueo.html
However, in the terms of use of Adachi Rei, it is written that the consonants included in Adachi Rei can be used in new sound sources if you indicate that you have used them.
In fact, there are a number of unattended sound sources created using Adachi Rei's consonant sets.
乃乃歌
電話歌キレ太
朝空マイ
There may be some consonants that can be used in English as well.
This may also be helpful.
声のようなものを作る【UTAU音源制作過程】