Coil drivers for the quad L2 (penultimate) stage have four dewhitening filter states, of which state 2 has the largest range and state 3 the lowest noise.

State 2 is meant for lock acquisition, and is not compatible with low noise data taking (unless some form of subtraction is used). As shown in the plot below, the DAC noise in state 2 would be expected to limit the historic DARM sensitivity in the 10-50 Hz band. (For ER9 sensitivity the state 2 noise is apparently low enough to be out of the way, as noted in alog 28107.)