Hi Everyone,

Last year I incorporated Bob McClure's inverse filter into WinQuake and WinSDR. See 
http://sites.google.com/site/bobmcclure90/inversefilter for more information on Bob's 
filter. You can try the filter in WinQuake if you install this beta release:

32-Bit: http://www.seismicnet.com/software/wq323b_32bit.exe
64-Bit: http://www.seismicnet.com/software/wq323b_64bit.exe

And if you have a PSN ADC board you can use the filter in real-time by using the 
current WinSDR beta release available here:
http://www.seismicnet.com/winsdr/winsdr4x.html.

Please Note! In WinQuake the pendulum frequency is entered in seconds so a 4.5 Hz 
geophone would be entered as 0.222. In WinSDR the frequency is entered in Hertz, so a 
20 second Lehman would be entered as .05. I should normalize this, I'm just not sure 
if I should change WinQuake or WinSDR...

In WinQuake the inverse filter can be found in the Time-Domain Filter dialog box and 
in WinSDR the Channel Settings -> Integrate / Filter tab dialog box.

A few days ago there were some emails on the list regarding what numbers to use for 
the pendulum frequency and high-pass filter. The pendulum frequency is the undamped 
period of your sensor. If you have a geophone this would normally be 4.5 Hz (WinSDR, 
..222 in WinQuake) or maybe 1 if you gave a 1 Hz geophone or AS1 type of sensor. This 
number sets where the filter starts to boost the lower frequencies to compensate for 
the drop off of sensitivity below the period of the sensor. The high-pass filter sets 
how much you want to extend the period of the sensor. It should be set to some number 
below the period of the sensor. Depending on the sensor and electronics, mainly the 
first op-amp, you might be able to extend the period by one decade.

Before adding the software filter to WinSDR and WinQuake I played around with the 
Robert's circuit. My results regarding using this filter, both in hardware and 
software, can be found here: http://www.seismicnet.com/epf/

Below is some information on the event files on my system that use this filter in WinSDR:

*.LCSV1.psn - This is a volume set from a Kinemetrics SV-1 5-Second 
intermediate-period vertical sensor. The LCZS1 channel is the raw data from the 
sensor. The LCZS2 channel has been period expended to 25 seconds (.04Hz) and then a 2 
pole 2 Hz low-pass filter is applied to the data. This helicoder plot (updated every 
5 min) http://www.seismicnet.com/quakes/images/lczs2.png shows the 24 hour graph from 
this channel. Teleseismic events show up much better on the inverse filter channel 
then the raw data channel.

*.LC45v.psn - This is a volume set from a horizontal 4.5 Hz geophone. The LCEG1 
channel is the raw data from the sensor and the LCEG2 channel has been period 
extended to 5 seconds or .2 Hz. This PSN event file
http://www.seismicnet.com/quakes/1201/120126.021845.lc45v.psn is a good example of an 
earthquake recorded from this sensor.

I would like to thank Bob McClure for supplying the Visual Basic code so I could add 
this feature to my programs.

Regards,
Larry Cochrane
Webtronics

On 2/6/2012 5:20 PM, Len Polucci wrote:
>
> Hi Chris,
> reading your response to David regarding Geoffreys inquiry about a damping resistor,
> you say that the Roberts circuit will lower the frequency response x 10 but I thought
> I read it was x 4 or 5 for a geophone? Do you know of ANY other 'bass boost' analog
> seismo amp? I do have Mariotti's EQ PCB unassembled,but I am wondering what it will
> do for an SP instrument with a natural period of 5 sec. Will it give me 25 sec. or 50
> possibly?*/
> /*
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