As the microseismic is back yet our recent ISIFF measurements suggested that the ITM FF filters were not working well, we updated those filters with new measurements.

Please see the first attached figure for the filter changes. The blue traces are the old filters and the red traces are the newly designed filters. The IX filters had a bit more structures in the 0.3-1 Hz band which hopefully would improve the subtraction of ISI motion. IY stays essentially the same as the previous one in the 0.3-1 Hz band. At the same time, both filters have much smaller gains in the sub-0.1 Hz band, which should reduce the amount tilt noise injection.

In the second figure we show the oplev response to ISI sus pt L motion with (red) and without (pink) the ISIFF. We show only the result for IY because the amount of reduction in IX is similar.

Will test the new FF filters with the IFO DOF like D/CHARD loops. Will also update the ETM filters once we have time.