Hi all,
 
  There has been recent discussion of inverse filtering, both analog  and 
digital. Chris Chapman has correctly noted:
 
    "The other problem is that the additional x100 gain at  0.5 Hz has to 
come from somewhere. If it is not provided by an auxiliary  amplifier, it will 
have to come from the main amplifier, probably reducing the  range and 
increasing the noise a bit. You also have the stepwise digitisation to  cope with. This 
can limit the accuracy of the compensation process. 
 
    If you had a signal of 1,000 counts at 4.5 Hz, there  will be just 10 
counts at 1/10 the frequency to do any compensation. Using an  additional 
compensation amplifier is likely to give better results. Lower signal  levels cannot 
be fully compensated - the digital signal is just not available -  unless you 
are either using a 24 bit ADC, or are using an oversampling technique  to 
increase the accuracy."
 
  If you should still want to try to extend the low frequency response  of a 
4.5Hz geophone, I have implemented a digital inverse filter which can  operate 
on PSN Type 4 files. The application is "WQFilter.exe". To download it,  go 
to 
 
   _http://www.jclahr.com/science/psn/mcclure/wdq_utilities/index.html_ 
(http://www.jclahr.com/science/psn/mcclure/wdq_utilities/index.html) 

and download the file "seismic_dataq.zip". Extract "WQFilter.exe" and  
"WQFilterHlp.txt" from the zip file.
 
  My personal opinion is that trying to use a 4.5Hz geophone is a  pretty 
futile exercise for most amateur seismologists, unless you have an  interest in 
local cultural noise or are sitting on top of an active volcano. I  use 
moderate period homebuilt sensors for my station. They range in natural  period from 
~5 seconds to ~15 seconds, and for them, the use of "WQFilter"  yields event 
waveforms closely resembling those recorded by professional long  period 
instruments. I use oversampling and DC amplifiers as well for data  acquisition.
 
Regards,
 
Bob
 





Hi all,
 
  There has been recent discussion of inverse filtering, both anal=
og=20
and digital. Chris Chapman has correctly noted:
 
    "The other problem is that the additional x100 gain=20=
at=20
0.5 Hz has to come from somewhere. If it is not provided by an auxiliary=20
amplifier, it will have to come from the main amplifier, probably reducing t=
he=20
range and increasing the noise a bit. You also have the stepwise digitisatio=
n to=20
cope with. This can limit the accuracy of the compensation process. 
 
    If you had a signal of 1,000 counts at 4.5 Hz, there=
=20
will be just 10 counts at 1/10 the frequency to do any compensation. Using a=
n=20
additional compensation amplifier is likely to give better results. Lower si=
gnal=20
levels cannot be fully compensated - the digital signal is just not availabl=
e -=20
unless you are either using a 24 bit ADC, or are using an oversampling techn=
ique=20
to increase the accuracy."
 
  If you should still want to try to extend the low frequency resp=
onse=20
of a 4.5Hz geophone, I have implemented a digital inverse filter which can=20
operate on PSN Type 4 files. The application is "WQFilter.exe". To download=20=
it,=20
go to 
 
   =
http://www.jclahr.com/science/psn/mcclure/wdq_utilities/index.html

and download the file "seismic_dataq.zip". Extract "WQFilter.exe" and=20
"WQFilterHlp.txt" from the zip file.
 
  My personal opinion is that trying to use a 4.5Hz geophone is a=20
pretty futile exercise for most amateur seismologists, unless you have an=20
interest in local cultural noise or are sitting on top of an active volcano.=
 I=20
use moderate period homebuilt sensors for my station. They range in natural=20
period from ~5 seconds to ~15 seconds, and for them, the use of "WQFilter"=20
yields event waveforms closely resembling those recorded by professional lon=
g=20
period instruments. I use oversampling and DC amplifiers as well for data=20
acquisition.
 
Regards,
 
Bob