Jenne, Hang

We added some extra ASC cutoff filters for C/DSOFT pitch and DHARD yaw, which improves the noise below 30 Hz. Please see the first attached plot.

For the SOFT pitch loops, we increased their bandwidths to suppress the 0.5 Hz oscillation. This made their noise showing up in DARM (see, e.g., LHO:44746). To suppress this we added an extra LP filter in their ctrl filter banks whose shape is shown in the second plot. The filter is in FM7 for DSOFT_P and in FM5 for CSOFT_P. In the third plot we show the SOFT PITCH loop shape after the new LP engaged.

We also put the LP engagement in the guardian LOWNOISE_ASC state, which worked fine.

The forth plot shows the noise projection of DSOFT P to DARM with the LP on. The ref traces (blue) were without injection and the nonref ones (red) were with noise injection. No significant contamination showed up in DARM above 20 Hz when we excited the output by a factor of ~ 100. The CSOFT P projection is essentially the same. Both measurements' raw data are attached as well.

In addition we also engaged the an extra LP in the DH_Y loop. The LP's shape is shown in the last figure. It is fine to engage such a filter as at the DH_Y UGF we have ~ 50 deg margin previously (LHO:44736).