To me it's kind of like a little quirk in the vocals that tends to come from the particular method of synthesis, but I'm not good at putting it into words. For example, Vocaloid specifically seems to add a kind of... edge, I guess, to the vocal. I remember one time I was talking on this forum about someone on Twitch recognizing an Oliver song as the same voice as Puppycat, and someone commented that when they watched Bee and Puppycat that they recognized Puppycat was a Vocaloid from the "weird envelope sound." If I had to guess I think it comes from the way the program splits up phonemes? But I'm definitely not technologically savvy enough to be sure or explain it well. It also seems to make vocals sound more nasally? Like it messes with the timbre of the voice provider's voice in the recordings in a specific way.
CeVIO, especially pre-AI, has like a... buzzy/shaky sound? UTAU, I'm not sure if what I think of when I think "UTAU engine noise" is really engine noise or noise from typically-not-professional-quality recordings. Honestly if I try to listen really hard I can kiiind of maaaybe hear a noise from Synth V, but it's so faint it's even harder to try to put into words, other than "It's simply not a real human, it's not going to sound perfectly like one."
All of that said, I don't think it's a big deal usually, I just felt like trying to put what "engine noise" means/sounds like to me in words X'P
CeVIO, especially pre-AI, has like a... buzzy/shaky sound? UTAU, I'm not sure if what I think of when I think "UTAU engine noise" is really engine noise or noise from typically-not-professional-quality recordings. Honestly if I try to listen really hard I can kiiind of maaaybe hear a noise from Synth V, but it's so faint it's even harder to try to put into words, other than "It's simply not a real human, it's not going to sound perfectly like one."
All of that said, I don't think it's a big deal usually, I just felt like trying to put what "engine noise" means/sounds like to me in words X'P
in voiceroid, is Voiceroid 1, ex sometimes the voice in some words sound like is drowning, the perfect example of this is spaming lines over a single vowel, since the vowel repeats you can hear a metalic noise of the program strugling to recreate that sound [あーーーーーーーーーーー]