In the AD e-book EDCh 8 (http://www.analog.com/library/analogDialogue/archives/43-09/EDCh%208%20filter.pdf) diagrams of example filters are given at pages 8.31 - 8.41. Page 8.29 tells what to do to scale these diagrams from -3db at 1 Hz to -3db at Fc Hz.
When looking with my Acrobat Reader, it reads "Denormalize the step response by dividing the time axis by 2pi Fc.
Something is missing. If I chose Fc=1, nothing is changed, but i shall divide the step response time axis with 2pi ?