"Key Follow" is a feature that allows the filter section to be adjusted automatically according to what notes are currently being played. This is very helpful in overcoming the sometimes drastic differences in sound and content of the varying notes on the keyboard as a result of filtering. For example, lets say you have a low-pass filter engaged and you have the frequency set low, you will notice that the higher you go in notes, the less coherent and precise the sounds become, due to the low-pass filter and the notes lack of low end content. Going into the edit parameters for the filter section and then using the page buttons to call up the "Key Follow" page and setting a positive value will help overcome this problem. Try it out and see.