Both do the same thing. But the software analysis can create the natural frequencies in the allocated range, does not investigate or check against your certain frequency.
You need to look at frequencies, at least first three, with +/- 25% range and check if your 4 Hz stays within those ranges. If so you need to change the piping frequency, otherwise pipe will be in resonance.
You need to make sure that 4 Hz of frequency is adequate for the application. Check API 618 latest edition.