SW forum:

I am trying to process time sample data in matlab in order to input into the selected base excitation frequency curve, I don't 100% understand what PSD is, how it works, and what units/normalized units, solidworks is expecting, I was thinking about using the periodogram function in matlab to return a PSD magnitude vector, however I am not sure how to match that with frequency vector, do you have any suggestions? thanks

There is pretty decent, albeit simplified, explanation in the dynamics training manual. The PSD one uses is usually an" enveloped" version of that you would compute for the PSD - that is to say the one computed is approximated as a set of straight lines bounding the computed PSD.