A interpolator which increase sampling rate by L times is followed by an anti-imaging filter, the filter is said to have a cutoff frequency of Fs/2L. Is Fs here is the frequency before or after interpolation?
Also during rational sampling rate conversion, the filter in between the interpolator and decimator is said to have cutoff at min(Fs/2L, Fs/2M). But clearly Fs isn't same for both of them. The interpolator changes the sampling rate before the signal passes through the decimator.