Hi Barry,

It sounds like you've been messing around with something similar to a 
project I started but didn't get around to finishing.  I added a 
waterfall FFT plot to my data logging program, but never finished 
debugging it.  In part because I wasn't all that confident that the plot 
would be worth all that much.

I'd be interested in a little more information regarding how you are 
collecting the FFT and some of the design decisions you use (number of 
samples in the window, how frequently you do a conversion, etc.)  Did 
you write your own code or are you using some 3'rd party software?

Larry Conklin
Liverpool, NY
lconklin@............


On 12/29/2009 12:12 AM, Barry Lotz wrote:
> 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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