I suggest that noise examples need an fft with
a frequency scale attached in order to tell whether
the noise is around 6 seconds period. Winquake
can provide this.

How about the noise example I posted last month?
Here it is again with both velocity and fft data.

http://www.infiltec.com/seismo/nois-amp.gif      velocity adc data
http://www.infiltec.com/seismo/nois-fft.gif          fft spectra

Although the velocity adc data does not show
any obvious periodicity, the fft does.   The data
is from my 18 sec Lehman with oil bath damping.         
There seems to be a peak in the spectra near
f=0.2 or 5 sec.  How broad should the 6 sec noise
spectral peak be?

Or am I just looking at the frequency response of
my system filtering random noise?

TIA,

Dave Saum

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