NMR in the silicon clathrate compounds NaxBaySi46 and NaxSi136

29Si, 23Na, 137Ba, and 135Ba NMR experiments were carried out in the superconducting silicon clathrate compound NaxBaySi46 to study the electronic states above the superconducting transition temperature. At all the atomic sites, considerable Knight shift and the Korringa relation in NMR relaxation were found, which indicates metallic electronic structure with moderate electronic correlation. The conduction-electron spin/charge density was found to be strongly site-dependent. The Na atoms are partially ionized as well as the Ba atoms, which shows noticeable difference from metal-doped fullerides. The results of comparative NMR experiments with non-superconducting clathrate compound NaxSi136 suggested that the existence of the Si site with remarkably large Knight shift in NaxBaySi46 has some relevance to the superconductivity.