Many audio apps hang in High Sierra after an upgrade from Sierra
Mine is caused by an audio unit. Removing it fixes the problem. User and system audio units are in the folders 


~/Library/Audio/Plug-Ins/Components/
/Library/Audio/Plug-Ins/Components/ (be careful when you change the system audio units)


Some other audio add-ons seem to cause similar problems according to this web page https://weblog.rogueamoeba.com/2017/09/29/fixing-an-important-high-sierra-incompatibility/