nearly all of the P4 ECMs use a knock filter integrated into the MEMCAL, the only one i can think of that doesn't is the 1227165, that uses the setup posted above.

then, when you get to the P66 modules, only the Northstar still had them integrated into the MEMCAL since it was the only unit that wasn't flash based. the rest used a seperate, removable knock filter.

the first set of OBD2 PCMs used the knock filter as well, but around ~1997/1998, the filter was removed entirely..... not sure how those PCMs account for knock frequency.