They probably affect wavelengths or something similar to that, if you want to tie it into the smooth vs sharp thing.
EDIT: But aside form my horrible terminology, this would cause a hos tof other problems neve rnoted in the book.
EDIT EDIT: Note that in one section, Joel mentions that he can speak normally, but can't yell without being dampened. So with range, the symbol doesn't weaken at all, but simply raises the bar fo rhow loud you can be, kind of like the triangle theory for a line of forbiddence. Interesting.