Digital BW, The Print

Can someone explain or point me to a source for reading about how to use this filter to 
minimize banding? I just Googled but diidn't find anythiing specific.

 Before I got my own 2200, I had a friend who works at the Photographic Workshops in 
Maine do some printing for me on his 2200. I saw that he used this filter but wasn't really 
paying attention. Now that I have my own 2200 I'd like to know what he did, as I often get 
banding in solid areas of midtone, and his prints were band-free.

Thank you!
Sarah