We had an oplev tuning party this afternoon. What we have learned is that we don't have a lot of intuition yet on tuning loops. But, that was part of the point - to build some intuition.
I took responsibility for the PRM, and Vivien took ITMX. I think, in the end, all changes were reverted on ITMX, however Vivien took some data to try and make a computer-generated controller. Before we got started, I locked and aligned the PRMI, and we centered the PRMI-relevant oplevs.
I moved my "boost bump" around a bit, to do more at higher frequencies, but had to sacrifice some of the "oomph", since it was starting to eat up too much phase at my UGF of ~8Hz. I also made the stack resonant gain higher Q and lower height so that it didn't eat so much phase. In the end, I have 25 degrees of phase margin, which isn't really great, but I do win a factor of 2 around 2 and 3 Hz. Also, now I'm able to engage the 3.2 resgain at all, whereas with the previous filter shape I was not able to turn it on.
Maybe it's because I really want it to have helped, but I feel like the POP spot isn't moving as much when I'm locked on PRMI sidebands as it was earlier (we were seeing a lot of low frequency (few Hz) motion). So, I think I did something good.