Though a completely valid take, it is very funny seeing the opinion 'I prefer Vocaloid Gumi because she sounds robotic', because if you'd dared say Gumi sounded robotic during the pre-AI era you would have been JUMPED
It's must be individual phoneme samples as i suggested, because i can't control full phrase voice since vocaloid engine is already synthesized. Any change in pitch and timing will affect formants quality (it may sound thin/hollow or it doesn't sound like Luka anymore) this mean a standard pitch shifting doesn't work that well.By "voice sample," do you mean the full phrase, or individual phoneme samples?
I use a modified circuit Yamaha TG33 it's a 90s-ish Vector synthesis, although a custom build sy22 or an1x, sq80 is work too (or anything that have CPU inside it) but i don't even think about modding these synthesizer since these synth are the relics from the past right now and should be keep it true to the original unit.Also, how do you morph manually--Melodyne?
I will inform who interested via inbox since this more like a private class Livestream. A very detailed breakdown (1-2Hrs+).