Plug-in Host Not Processing with AUs, Works fine with VST

I built a small host in which I will pipe in data manually to a plug-in.  I can create the plug-ins and GUI's fine for both AUs and VSTs, but when I call processBlock on the AUs, it does not work (it runs much faster (almost instant) than the VST version of the same plug-in -- it is calling AudioUnitRender ).  Is there another function that must be called to initialize AUs (I am also calling setPlayConfigDetails and prepareToPlay - both do not seem to help at all)?




It turns out that for AudioUnits the prepareToPlay needs to match the number of samples that you give it whereas for vst, you could vary the number of samples in the processBlock().