If I can play a song right away without even trying much, I won't add DD because I figure that if I can play it, everyone else can, too. When I add DD I do it manually. I've tried the DDC and it just never worked right for me. Maybe I'm just not giving it the right input, but the output always seems weird to me. When I do it by hand, I look at the note pattern and try to get an understanding what the actual difficulty is. Then I try to tone that done, one step at the time. I don't usually do more than four levels. It took a pretty long time for the first song I did this for, but when I did it the last time, I was much faster. And I was lucky enough to have selected notes to play for the easy difficulties that still make the song recognizable and fun to play - or so I hope.