
SouthSIDE Glen
independentrecording.net
A shelf and a roll off are not the same thing.giraffe said:"roll off" is a bit of a loose term that can refer to (at least in my head)
a low/hi pass (like you have shown) or a subtractive low or high shelf, like i tried to explain.
As tarnation correctly said and showed, a roll off lo/high pass keeps increasing the amount of gain change as the frequency increases (or decreases, for a high pass).
A shelf, OTOH, has a set gain change level that it slopes to and then holds there regardless of frequency extent. That's one of the origins of the term "shelf"; graphically it resembles a flat level shelf. A "roll off", however, keeps rolling off towards the bottom of the graphic frequency chart and doesn not flatten out.
Additionally, a shelf can refer to a boost or a cut, whereas a roll off is an overall cut only.
Note that some roll off filters can actually have a bit of a bump at the set frequency before rolling off, but that's an occasional design detail that one shouldn't let confuse the general description given before.
G.