Joe is Sara's upbeat best friend who's more childish personality servers as a nice contrast to Sara's more mature attitude while still being just as dependable.
Joe probably has a pretty typical higher pitch best friend kind of voice thats loud and expressive

(Spoiler warning)
Joe is also seen later in the story as a hallucination Sara experiences after Joe's death. This version of Joe is cruel and unforgiving and torment Sara by calling her a murderer.
With that in mind Joe needs to also be able to sound malicious with his tone in a way that makes him feel tonally different from the real Joe