You can do a similar thing with the sound
program AUDACITY but you find it will
take out everything even your signal
if not careful.
Narrow band is the best way to beat noise.
Look only in the area of the spectrum
that contains the signals you want.

CLIP a piece of noise then remove that same
noise over the entire data.
It removes best at the very place
it was clipped from and sporadic
everywhere else.

It might be good to to have two seperate amplifiers
one for regional and one for teleseismic
they overlap but are not identical.
If noise is at the same freq even if alised it can
not be removed as far as I know without
affecting your signal too.

An fft might be best at seeing things alone
but it takes a span of time to see such
a signal so your time resolution/precision
is possibly destroyed.

The original signal is best without too much
filtering.

Just try and get the noise low and uniform
and the signal should stick out like
a sore thumb even if it does not
look pretty like the scientist want.


----- Original Message ----- 
From: "Barry Lotz" 
To: 
Sent: Monday, December 28, 2009 10:12 PM
Subject: Sensor noise


All
I have successfully used a running fft to sense signal frequency component changes and used this as a trigger mechanism for an 
event. Could one use the ( I guess you call it ) power spectrum of the signal just before and during the event to remove the noise? 
I guess you would have to use the same time window so the frequencies would compare. Could it be a simple subtraction of the 
"before" from the "during"? This would assume that the background noise didn't change in the period during an event. This could be 
better than trying to shape a multi pole filter to eliminate the noise. I have found that often a portion of the event signal is in 
the same frequency range as the noise.

Regards
Barry
http://www.seismicvault.com 

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