As Corey and Kiwmau noted, ETMY has 2 violin mode harmonics fairly close to each other (1008.45 and 1008.49). ETMY MODE3 has been set up to damp the higher frequency one with a broad bandpass, a phase of +60 and a gain of +100 set in the guardian (FM1,3,4,10, total phase at 1008 is 82 degrees). Cheryl looked at the DARM spectrum over some of the long locks recently, and it seems that with these settings the lower frequency one 1008.45 has slowly rung up.
The phase shifting filter modules also had 6 dB of gain, which cause some unintended saturations, so I edited them to have 0 dB of gain at 1008.45 Hz. We addded two stop bands to the filter bank, one for 1008.493 and one for 1008.45 Hz.
After some confusion, we have been able to slowly damp this with a positive gain and FM1,2,4,5 (the new notch) ,and 10 on. This means a total phase of -75 degrees. This is not ringing up any other modes that we can see so far.
So for now:
The damping of both of these modes are commented out in the guardian, so it will only be damped if you engage one or the other by hand.
To damp 1008.49Hz use FM1 (broad bandpass at 1010), 3 (+60 degrees phase),4 (100dB), FM6 (to notch the 1008.45 mode), FM10 to notch 1009.6 mode and a positive gain
To damp 1008.45 use FM1,FM2 (-60 degrees) FM4, FM5 (to notch 1008.49Hz) and FM10 and a positive gain.
We can make two different filters to damp these two modes simulateously in the future.
This configuration causes the mode at 1009.03 Hz to ring up. Note that this mode already has its own dedicated damping FM (MODE7).
I added a stopband for this frequency in the MODE3 filter module. So far both modes (1008.45 Hz and 1009.03 Hz) are damping simultaneously now.
Damping the 1008.45 Hz mode with MODE3 was very slow going, so I implemented a separate damping loop using MODE9 and the following settings: FM1, FM2, FM4, FM9, positive gain, and length drive to the PUM (instead of pitch). This seems to be somewhat faster than before, but still much slower than some of our other damping loops. Anyway, the ADC counts for the DCPDs are topping out around 25000 ct in full lock with 1 stage of whitening (the limit is 32000 ct), so this is enough to proceed to nominal low noise. The mode should continue to damp down if we can maintain lock with these new damping settings.
To keep the 1008.49 Hz mode from ringing up again, I have turned on MODE3 with the settings that Sheila described above: FM1, FM3, FM4, FM6, FM9, FM10, positive gain, and pitch drive to the PUM.
As before, these settings will NOT engage automatically during lock acquisition. However, since we accepted these settings in SDF, either the loops will need to be engaged by hand, or new SDF settings accepted.
The Violin Mode Table has been updated. From what I have in my note, ETMY MODE3 filter has always been turned on by Guardian. I have the same question as Dan, what changes?