  We report a comprehensive study of the complex AC conductance of amorphous
superconducting InO$_x$ thin films. Using a novel broadband microwave `Corbino'
spectrometer we measure the explicit frequency dependency of the complex
conductance and the phase stiffness over a range from 0.21 GHz to 15 GHz at
temperatures down to 350 mK. Dynamic AC measurements are sensitive to the
temporal correlations of the superconducting order parameter in the fluctuation
range above $T_c$. Among other aspects, we explicitly demonstrate the critical
slowing down of the characteristic fluctuation rate on the approach to the
superconducting state and show that its behavior is consistent with vortex-like
phase fluctuations and a phase ordering scenario of the transition.
