I have to agree with James. I use FsInn for vatsim and have no problems with voice. Check you sound settings as James suggested and if that doesnt work then i would give FsInn and FsCopilot a try. There is a little learning curve to it but has a lot of features the SB doesnt. I have never used SB4 since it wasnt even out when I started fly fsx on vatsim.