GNormal tries to remedy denormal problems by introducing extremely low-level noise to the signal path. (If you don't know what that means, then you probably don't need it).
Some CPUs employ techniques to extend the accuracy of floating-point calculations for very small numbers. These small numbers are called denormals.
Unfortunately, calculations involving denormals can be very slow. This can drastically affect audio DSP performance. In most cases, these numbers are too small to be of any interest anyway.
Adding noise to the signal path can sometimes prevent denormals from getting into subsequent calculations. Obviously, the noise-level used is so low that you cannot hear it.
The simplest way to configure GNormal is to place it before a suspect plug-in and set the Level parameter to maximum. Try each setting of the Type parameter to see if the problem goes away. When you have found a suitable noise-type, you can try lowering the Level.