The filter is just the time domain filter tool in Winquake.  The 
combination of a 2 hz low-pass and a 0.4 hz high-pass, both Butterworth 
if the info presented in the Winquake filter box is accurate.

I don't see anything remarkable in the unfiltered data that looks 
particularly pulse like in the vicinity of the chirps, but the record 
does in fact contain two sharp transients later in the window that are 
nowhere near either of the "chirps".

But the real kicker is when you listen to speeded up sound files derived 
from both the unfiltered data and the bandpass filtered data.  You hear 
the background hiss and crackle, and then you hear "bweeeooop" .... 
"bweeeooop".  followed eventually by a couple of pops where the 
unrelated transients occur.  And no pulse like sounds preceding the 
"chirps" at all.  The sound files are very speeded up versions of the 
original data.  The hour long event file results in a sound file that 
takes arount 15 seconds to play.

The chirps are very obvious when you listen to the files, but you would 
never recognize them in the unfiltered time record and I only noticed 
them in the filtered data because I was already looking at the vicinity 
if the Winquake predicted S wave.  The chirp at that spot looks like a 
candidate for the S onset untill you expand it enough the see the 
waveform, and then it is obvious that it isn't seismic.

Larry

On 7/23/2011 6:04 PM, Mark Robinson wrote:
> This is what you will see when a pulse goes through a filter.
>
> Without knowledge of the exact nature of the filter it is difficult to 
> know exactly how it will behave, but in general you will get a time 
> delay and often extreme phase effects.
>
> So while the chirp may appear to precede the signal, it may be the 
> signal which is delayed by the filter, and the chirp may be a filter 
> artefact aligned with the initial arrival.
>
> It could also be a local electrical pulse (anything being switched on 
> or off) making the filter ring, so you could try plugging something 
> noisy into the same mains outlet and switching it on and off to see if 
> you can induce the same behaviour.
>
>
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