Just to clarify: the shape of the FT may certainly change when you change kmax. But if the data and the model change in the same way, then the fit is insensitive to the choice of kmax, in the sense that the fitted parameters remain stable to within their reported uncertainties. —Scott Calvin Sarah Lawrence College On Aug 4, 2016, at 2:50 PM, Fuxiang Zhang mailto:zhangfx@umich.edu> wrote: The Kmax effect on the shape of magnitude of FTs of one of my samples may come from the low signal/noise ratio.