Jeff K. emailed me about a suspicion that the digital whitening compensation for the ETMy oplev was incorrect, so I took a quick drive to End Y to check. Sure enough, instead of the 2 whitening filters and 0dB of gain enabled as indicated in T1500556 (and as would be assumed from the 2 compensation filters enabled in MEDM), 1 whitening filter and 3dB of gain was enabled. I corrected this, and the whitening filters and gain now match T1500556, with the proper number of compensation filters (2) enabled via MEDM. The attached pictures show the Output Configuration Switch (OCS) as I found it and as it should be. With the loss of 3dB of whitening gain, the SUM counts dropped from ~13k to ~9k.
Edited to add ISC and SUS tags.
Now the ETMY transfer functions are consistent with the other test masses.
The only remaining difference is now ITMY, which is a about a factor 2.3 smaller than the others.
Also, the phase of the ITMY transfer function rotates at low frequency. Maybe there is whitening issue with ITMY too?
