https://services.ligo-la.caltech.edu/FRS/show_bug.cgi?id=6031

https://dcc.ligo.org/cgi-bin/private/DocDB/ShowDocument?docid=E1600252&version=

We forgot about this modification that was done at LLO, therefore our OMC DCPD dark noise (only 1 stage of whitening, whitening gain = 0dB, HighZ) is still dominated by ADC noise for f<60Hz or so. See attached and compare with LLO plot in https://alog.ligo-la.caltech.edu/aLOG/index.php?callRep=27556.

This modification will use the second stage of the OMC DCPD whitening as an anti-whitening such that the stage 1+2 will act as a low-frequency whitening zp([1,500];[10,50]) without amplifying the violin in analog. This way we can enable all stages to get more whitening in low frequency without worrying about violin saturating ADC.

(After the modification, CAL group should make a careful analog measurement.)