Hi Ted,
 
I have been looking at your event files, and your filtering does not make  
any sense to me. For example file 070902.011039.tcidf.psn show the following  
filters applied:
 
1. IIR Filter BW LP Freq: 0.1 Hz  Poles: 2 
2. IIR Filter BW HP  Freq: 1 Hz  Poles: 2
 
The first filter attenuates frequencies higher than 0.1 Hz.
The second  filter attenuates frequencies lower than 1.0 Hz.
 
The usual filtering is to apply a lowpass filter to attenuate frequencies  
greater than 1 Hz, and a highpass filter to attentuate frequencies lower than,  
say, 0.05 Hz. The result is a bandpass filter for frequencies over the range 
of  0.05 Hz to 1 Hz. What you have done is to essentially exclude almost all  
frequencies, leaving a tiny response within the 0.1 to 1 Hz interval. The very  
low amplitude of your waveform after filtering confirms my belief. Your LP  
cutoff frequency should be higher, not lower, than your HP cutoff.
 
Please download and inspect my file 070902.0115.rem.psn to see the  filtering 
I used for the same event. The filtering for channel z reads:
 
1. Sensor Period: 4.52s Sensor Q: 0.7 Filtered Period: 40s
2.  Butterworth Order 2 HighPass backward Corner Period: 40s
3. Butterworth Order  2 LowPass dblpass-no lag Corner Period: 1s
 
These filters are my own design, and are available in my utility WinQuake  
filter utility, WQFilter.exe.

The first filter extends the natural period of my vertical sensor from  4.5 
seconds to 40 seconds.
 
The second filter is a special highpass filter excluding frequencies less  
than 0.025 Hz and executed backward in time. 
 
The third filter is executed both forward in time and backward in time and  
excludes frequencies greater than 1 Hz. The end result of my filtering is a  
passband extending from 0.025 Hz to 1.0 Hz, without any time delay or phase  
shift introduced.
 
Could you email me an unfiltered version of 070902.011039.tcidf.psn? Also,  
please describe your vertical sensor and its measured or estimated natural  
period and damping. I would like to try my own filtering on it.
 
Cheers,
 
Bob



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http://discover.aol.com/memed/aolcom30tour





Hi Ted,
 
I have been looking at your event files, and your filtering does not ma=
ke=20
any sense to me. For example file 070902.011039.tcidf.psn show the following=
=20
filters applied:
 
1. IIR Filter BW LP Freq: 0.1 Hz  Poles: 2 
2. IIR Filter BW HP=
=20
Freq: 1 Hz  Poles: 2
 
The first filter attenuates frequencies higher than 0.1 Hz.
The seco=
nd=20
filter attenuates frequencies lower than 1.0 Hz.
 
The usual filtering is to apply a lowpass filter to attenuate frequenci=
es=20
greater than 1 Hz, and a highpass filter to attentuate frequencies lower tha=
n,=20
say, 0.05 Hz. The result is a bandpass filter for frequencies over the range=
 of=20
0.05 Hz to 1 Hz. What you have done is to essentially exclude almost all=20
frequencies, leaving a tiny response within the 0.1 to 1 Hz interval. The ve=
ry=20
low amplitude of your waveform after filtering confirms my belief. Your LP=20
cutoff frequency should be higher, not lower, than your HP cutoff.
 
Please download and inspect my file 070902.0115.rem.psn to see the=20
filtering I used for the same event. The filtering for channel z reads:
 
1. Sensor Period: 4.52s Sensor Q: 0.7 Filtered Period: 40s
2.=20
Butterworth Order 2 HighPass backward Corner Period: 40s
3. Butterworth O=
rder=20
2 LowPass dblpass-no lag Corner Period: 1s
 
These filters are my own design, and are available in my utility WinQua=
ke=20
filter utility, WQFilter.exe.

The first filter extends the natural period of my vertical sensor f=
rom=20
4.5 seconds to 40 seconds.
 
The second filter is a special highpass filter excluding frequencies le=
ss=20
than 0.025 Hz and executed backward in time. 
 
The third filter is executed both forward in time and backward in time=20=
and=20
excludes frequencies greater than 1 Hz. The end result of my filtering is a=20
passband extending from 0.025 Hz to 1.0 Hz, without any time delay or phase=20
shift introduced.
 
Could you email me an unfiltered version of 070902.011039.tcidf.psn? Al=
so,=20
please describe your vertical sensor and its measured or estimated natural=20
period and damping. I would like to try my own filtering on it.
 
Cheers,
 
Bob


Get=
 a sneak peek of the all-new AOL.com.