The MICH feedforward path into DARM has been retuned, since Gabriele recently found a nontrivial amount of coupling from 50 to 200 Hz.
First, the MICH → DARM and MICHFF → DARM paths were measured according to the prescription given here. Then the ratio of these TFs was vectfitted and loaded into FM4 of LSC-MICHFF. This is meant to stand in place of FM5, which is the old frequency-dependent compensation filter. The necessary feedforward gain has been absorbed into FM4, so the filter module gain should now be 1. These changes have been written into the LSC_FF state in the Guardian.
Details
The attachment shows the performance of the new retuning compared to the old retuning. At the start of this exercise, I had already changed the FM gain of the "old" retuning from 0.038 (in the Guardian) to 0.045, as this removed a lot of the coherence near 100 Hz.
Also, I had previously widened the violin stopband in BS M2 L, but had not propagated this change to the analogous filter in LSC-MICHFF. This is now fixed. Also note that if any change is made to the invBS compensation filter in BS M3 L, this change must be propagated to LSC-MICHFF as well.
I did not have time to implement SRCL feedforward. I suspect it would be a quick job, and could be done parasitically with other tweaking activities.
Coherence between MICH and DARM before and after Evan's work. (As far as I can tell, yes, DARM got better and the range improved..although it is not evident from the SNSH channel, as it had problems around the time of Evan's work.) Let's see how much this coupling changes over time.
The LSC-MICHFF_TRAMP is now set to 3 versus the snap setting of 5 sec. This shows in the LSC SDF diff Table now and should be reverted or accepted, Evan?
Snap setting of 5 seconds is probably better.