J. Kissel, G. Vajente
ECR E2400116
IIET 30863
WP 11797

After yesterday's infrastructure changes to the H1 SUS OMC front-end model (LHO:76856 and LHO:76894), which moved the OMC ASC control signals
    - from going 
        . straight from the OMC ASC 2k model 
        . through the SUS-OMC_M1_ASC filter bank for plant compensation, and 
        . then out to EUL2OSEM matrix for basis transformation to the DAC 
    - to going 
        . from the OMC ASC 2k model
        . through the SUS-OMC_M2_ISCINF filter bank (for proper 2k to 16 kHz anti-imaging), 
        . through the SUS-OMC_M1_LOCK filter bank (for the same filtering that was done by the former M1_ASC bank),  
        . through the the SUS-OMC_M1_DRIVEALIGN matrix (though configured at the moment to no do any off-diagonal decoupling), and 
        . *then* out to EUL2OSEM matrix for basis transformation to the DAC

there was some worried that the excess noise between 10 and 100 Hz might be this infrastructure change.

It's not, as far as we can tell, responsible for and change in the noise in DARM.
In LHO:76928, Gabriele posted an ASD of the SUS-OMC_M1_MASTER_OUT_DQ channels to confirm that the drive to the OMC SUS's DAC is the same (the thought being that if the DAC request is drastically different, then we should be suspicious of the infrastructure change).

Here, in the attached ASD I show a different perspective -- the input to the former M1_ASC bank compared with the current M1_LOCK bank in pitch and yaw, and then showing those channels' coherence with DARM.
I compare 25 averages (0.02 Hz frequency resolution, 50% overlap) two times, 
    RED 2024-04-02 6:00 UTC Pre-change (in the middle of a good overnight lock stretch; 2024-04-01 23:00 PDT)
    BLUE 2024-04-03 18:05 UTC Post-change (in the middle of a good lock stretch this afternoon, though in the middle of SQZ tuning of ZM alignment)

This ASD also focuses on where the control signal is real signal (from the very slow loop design -- see LHO:65861).

While the character of the ASD control signal and coherence with DARM has changed around the (presumably OMC SUS) resonances, this perspective corroborates that we don't see substantial change. *Maybe* the change in character around the resonances changed because I misinterpreted the former infrastructure, and somehow we *were* using the confused DRIVEALIGN gain values from LHO:47488, but I think not.