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Entry  Fri Nov 25 22:11:12 2011, Mirko, Update, CDS, Beware of fancy filter modules ChebyTST3.pngCheby.pngCoherenceCheby.pdfChebyAt16kHzBlackand2kHzRed.png
    Reply  Sat Nov 26 02:05:43 2011, Mirko, Update, CDS, Beware of fancy filter modules 
       Reply  Sat Nov 26 10:55:40 2011, rana, Update, CDS, Beware of fancy filter modules 
          Reply  Mon Nov 28 19:24:51 2011, Jenne, Update, CDS, Beware of fancy filter modules SUSPOS_ETMY_30and0_measured_vs_idealTF.pdfSUSPOS_ETMY_Cheby_measured_vs_idealTF.pdfSUSPOS_ETMY_30and0andCheby_measured_vs_idealTF.pdfSUSPOS_ETMY_30and0andCheby_compareCoherence.pdfSUSPOS_ETMY_30and0andCheby_compareCoherence.pdf
             Reply  Mon Nov 28 22:09:24 2011, rana, Update, CDS, Beware of fancy filter modules noise.pdf
                Reply  Tue Nov 29 15:30:01 2011, jamie, Update, CDS, location of currently used filter function 
                   Reply  Tue Nov 29 15:57:43 2011, Den, Update, CDS, location of currently used filter function 
Message ID: 6031     Entry time: Mon Nov 28 22:09:24 2011     In reply to: 6030     Reply to this: 6037
Author: rana 
Type: Update 
Category: CDS 
Subject: Beware of fancy filter modules 

To see what might be causing the problem, I used a version of the filter noise test matlab code that Matt had in the elog.

To see if it was a single precision problem, I just recast the input data:   x = single(x)

This is not strictly correct, since some of the rest of the operations are as double precision, but I think that attached plot shows that a casting from double to single is close to the right amount of noise to explain our excess noise problem in the 0.1-1 Hz region.

Den is going to interview Alex to find out if we have some kind of issue like this. My understanding was that all of our filter module calculations were being done in double precision (64 bit), but its possible that some single stuff has crept back in. Currently the FIR filtering code IS single precision and in the past, the SUS code which didn't carry the LSC signals (meaning ASC and damping) were done in single precision.

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noise.pdf
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