I'm not sure as I'm not familiar with the psp3, but it seems like it is some sort of phase switch (duh). if you just running mics into a 2 channel recorder then the switch may not really matter. if there is a seperate phase switch for each channel, then you will notice a difference if it was switched on one channel and not the other. If you were running this pre into say a 4 channel recorder, then the psp3 would have been out of phase with the other channels on the recorder, thus noticing a big difference. But if you have only one phase switch for the entire psp3 and thats all you were recording then no, you wouldn't really notice a difference.