In our DARM noise budget, both SRCL and MICH noises are higher than they were during O2, and are limiting our noise right now.  Here I am just summarizing some information about the SRCL noise.  

In the first attachment, you can see that the coupling of SRCL control signal without feedforward on is very similar now to what we had in June 2017 (blue and green traces).  The brown and pink traces show the coupling with feedforward on, you can see that the feedforward now is actually doing a slightly better job than we were doing in O2 from 40-100 Hz.  

In the second attachment, you can see that the SRCL control signal is now larger than it was in O2.  The lower panel shows the signal out of the sensor.  We changed the whitening gain from 30dB to 21dB, (we now compensate for the whitening gain in the digital gain but we didn't in O2, the gain change is corrected for in this plot). 

Above 70 Hz, the control signal is about a factor of 2 above what it was in O2.  This makes sense, because our UGF is about a factor of 2 higher than it was in O2.  (See 3rd and 4th attachments, and the OLG posted by Evan Hall here: 24933) 

Below 70Hz or so, there is excess noise.  Much of this noise is due to HAM3 motion (see Georgia's measurement in 44393 and the comment from Hang).  We were able to reduce this noise in SRCL by tuning the PRCL subtraction in the input matrix (44893), however, the tuning seems to be changing from lock to lock so that we are not able to use a consistent input matrix to get rid of this noise.