Following 23900. The attached figure shows coherence among OMC-DC (aka DARM), MICH, and PRCL after applying the feed forward (FF). As seen, most of such coherence in the important frequency region (say 50-1000 Hz) reduced, other than particular features around 200 Hz, which would be discussed in the another post later; maybe FF won't deal with these features. As mentioned in 23900, we may need to do further fine tuning of the FF filters in the end of the days, but it may not be a game changer any more.

With the application of these FF, we have used up all (or most?) of the legacy of O3GK for length-sensing control. This is the entry point into the deep forest, the real commissioning.