I believe that his semblance is one of 2
1-Calm mind. For someone who hasnt been in a fight he isnt scared when he is fighting. Keeping a calm mind in a fight is a quality that all leaders must have, that way its easier to make decisions in the middle of a fight.
2-"Hero State". Have you seen avatar: the last airbender/the legend of korra? Maybe Jaune can talk or connect to other heroes the same way Aang and Korra did. Jaune comes from a family of heroes, his father, grandfather, andfather before him were all heroes. He always wanted to be a warrior and as far as i can remember he doesnt say why. Maybe his subconcious knows what to do in battle and helps him, but since he doesnt have a warriors body there is a limit to what he can do. This semblance even goes along better than most because of Jaune's "theme", Joan Arc. Maybe he instead of hearing god like Joan, he hears the voice of warriors in his bloodline. Maybe he can draw the experience from them and become a warrior. That would also explain why everyone in his family before him are warriors. His semblance is hereditary just like weiss (and maybe Raven). It would also explain why tyrian has interest in him, he feels that jaune has a lot of aura because is the aura from other warriors, he might feel other people's aura.
As for the more common theories: -Voice buff: Nah, doesnt explain why he fits right on this scene -Super Shield: Same reason as above, we see Ren use Shield-like ability before. The scene that shows Jaune do the Super shield can also be explained by a burst of his aura due to his anger.
Those are my thoughts.