Quote Originally Posted by Khaalis View Post
… Yet all I get is this washed out wavy noise:
Most likely, there are one or more points that are of fairly large magnitude on your surface. This can happen if your mask wasn't hard-edged (masks can be fixed in Wilbur with Select>>Modify>>Binarize). What happens is that if the selection isn't hard-edged, filling the surface with a large value may result in a semi-large value along the edge that can be greater than the magnitude of your attempted fractal noise. I mentioned the smooth edges thing because your first Wilbur image has brown edges, which would indicate that the selection isn't fully hard-edged.

One way to look at your surface altitude distributions is with Window>>Histogram. You should see a fairly narrow distribution and probably a few outliers. Filter>>Height Clip can be used to clip off the outliers to get a better result.