Raw MIDI shifting can sound quite unnatural. No human singer is capable of the extremely fast pitch transitions that you can achieve by sending the VoiceOne a series of MIDI notes.
One of the most obvious ways to naturalize MIDI shifting is to smooth out the pitch transitions. Inflection - Portamento is the VoiceOne features that accomplishes this. Go to the inflection menu and choose the style called “Portamnto”. Dial the amount to suit.
Another source of unnaturalness happens when using MIDI to sustain a note for a long period of time. No human singer is capable of sustaining a dead-on accurate pitch for the indefinite periods of time that VoiceOne allows.
Adding vibrato is the best way to naturalize long sustained notes.
Alternative to both methods, you could tweak an external pitch-bend stick for manually controlled vibrato and scooping.