Pandemonium takes inspiration from the classic Sonic the Hedgehog manga! Because of this, Sonic isn't his own character, but instead the alter ego of a schoolboy named Nicky. Nicky is a shy little hedgehog who, at the beginning of the series, heavily looks up to his classmate and friend, Mighty the Armadillo. As the series goes on, he gains confidence and is way more sure of himself. However, he's never as confident as he is when he's Sonic the Hedgehog. As Sonic, Nicky feels like he's on top of the world and can do absolutely anything.
Nicky should sound like a Sonic that's down on his luck, timid and not very sure of himself. Think the normal shy boy voice, but with a Sonic spin! Nicky as Sonic should just sound like Sonic, Bear in mind, Season 1 of Pandemonium is adapting SegaSonic, Sonic 1 and Sonic CD., so I'd suggest going for a Jaleel White or Martin Burke Sonic voice (Burke preference). Feel free to do your own fanon voice if you believe it'll fit the character!