AudioUnit渲染回调调用在iPhone模拟器上，但不是在电话上

I have a fairly straightforward setup in which a RemoteIO unit is taking input, doing a bit of processing, sending it out the output, and writing the output to a file. Right now, I'm just generating test signals inside of my RemoteIO render callback, so I don't really care about anything coming from the 'actual' input. My render callback is called and works a treat in the simulator, but is never called at all when run on the phone. Any ideas where I should start looking? Am happy to post code--just not sure what everyone would like to see...I have a fairly straightforward setup in which