I have used this program before.
http://www.visualizationsoftware.com/gram.html
 It used to be free but you can still find older free versions on download sites.

Jim Hannon


---------- Original Message ----------------------------------
From: John or Jan Lahr 
Reply-To: psn-l@..............
Date:  Fri, 25 Feb 2005 07:19:42 -0800

>
>
>Hi Jack,


>We used "spectrograms" of the sort that you described in
>studying the 1989-1990 eruption of Mt. Redoubt, Alaska.  They were
>the best method that we found to monitor and distinguish "LP"
>events (with emergent arrivals and lower frequency content) from
>"VT" events (volcano-tectonic events with higher-frequency
>content and sharp arrivals).  Swarms of LP events tended to precede
>eruptions.


>It would be great to have a tool available to amateur seismologists and
>educators that would allow spectrograms to be easily generated.  Do
>you think this could be done without the use of Matlab?


>Cheers,

>John


>
--
Jim Hannon
http://www.fmtcs.com/web/jmhannon/
42,11.90N,91,39.26W
WB0TXL
--

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