A versatile multiscale theoretical approach for the viscoelasticity of the homogeneous rubber matrix has been established taking into account relaxation processes at different time and length scales as well as nonpolymeric relaxation processes at extremely high frequencies. It allows to fit and describe the dynamic moduli of unfilled S-SBR rubbers over 16 frequency decades with a limited set of parameters (relaxation times, scaling exponents) which have a clear physical meaning and obey the relations motivated by the statistical physical theory of polymer melts and polymer networks.