I can't imagine ever wanting to restart my island because of all the catalog unlocks, but I could see myself deleting some islanders eventually to bring in new ones.
For creating voices:
Pitch is obviously how high the voice is.
Speed is self-explanatory, but you can tweak it slightly to try to get rid of random glitchy sounds in some voices.
Quality, from left to right, is like old man -> deep voice -> more whiny male voice -> female -> raspy old lady.
Tone is how high their voice is at the start of a sentence. Higher is more expressive-sounding while all the way left is monotone and almost robotic.
Accent can be tricky to get sounding right, I think it actually adjusts reverb. I usually keep it low, but a far right Accent combined with Intonation 3 or 4 can lend itself to faux-foreign accents.
Intonation 1 = slightly monotone, 2 = upward inflection (like everything is a question,)
3 and 4 both sound overall more expressive in slightly different ways.
I mostly set the intonation and speed, then just play around with mostly Pitch, Quality, and Tone until it sounds close to how I think the person sounds.
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