The DTT template for showing the MICH spectrum on the control room wall is suffering from leakage, preventing us from seeing some features in the 8 to 11 Hz range. The current parameters and window are:
Window: Hanning
Start/end frequencies: 0/74444Hz
BW: 0.1Hz
Overlap: 70%
Avarages: 3
Resulting BW: 0.18Hz
After playing with the available windows (but keeping all other parameters fixed so it will refresh with the same latency), I have found that Flat-Top reduces the resulting BW to 0.24Hz but also reduces the leakage problem. This would allow us to see features over the problematic range. The first two attached figures correspond to 2015-10-28 14:48:24 ; they show how the Hanning window suffers from a real leakage problem while Flat-top maintains it’s performance. The feature over 8Hz corresponds to a problem solved by Bubba on log (22939).
I rather prefere to change the whitening filter, instead of chaging the windowing method.
Jeff and Miquel changed the DTT template displaying MICH, the new parameters and window are:
Window: Flat-Top
Start/end frequencies: 0/74444Hz
BW: 0.08Hz
Overlap: 70%
Avarages: 3
Resulting BW: 0.235628Hz
We believe that changing the whitening filter will not solve this leakege problem. The Hanning window resolves the frequency location better i.e smaller *BW but it's error in amplitude is up to 16%, whereas the FlatTop window measures better amplitude there for in this case reduses the leakege problem.