PSN-L Email List Message

Subject: STFT and PSD
From: John or Jan Lahr JohnJan@........
Date: Sat, 10 Feb 2007 10:48:31 -0800


The STFT sounds useful, but I'm not sure what it is.

Also, could you share your spread sheet for computing the PSD?  That
quantity has always left me scratching my head.  Maybe if I played around
with it a bit, I would be able to appreciate/understand it better.


At 08:30 AM 2/10/2007, you wrote:
>Thanks, Bob, for pointing this out to me.
>    I downloaded the update and now have this very useful feature of selecting
>between linear and log-log plots of spectra.  This increases the 
>flexibility of
>Amaseis considerably, especially in the low frequency realm where I 
>hope that many
>of you will follow Allan Coleman's lead.  Kudo's to Alan Jones for 
>providing this
>additional capability to his outstanding software.
>Incidently, I have been using Amaseis to both collect and analyze 
>some pendulum
>data as part of my research of low-level anharmonicity.  Those who 
>are interested
>might want to look at the Mercer Physics department webpage 
>announcement concerning
>the seminar I will be giving next week
>      Something I just noted (don't know whether it was available on 
> the earlier
>version of Amaseis)--is a very useful additional feature of the 
>code; i.e., the
>ability to read-off (by cursor placement with the mouse) the FFT 
>magnitude as well
>as the frequency of a spectral line.  This is of great value when it comes to
>estimating the quality factor of a pendulum in free-decay using the so-called
>"short time-Fourier-transform" (STFT).  One can 'step through' the 
>record manually
>to accomplish what is typically an automated process as in routines 
>like LabView.
>    About my comments concerning the synergy of Amaseis and WinQuake when used
>interchangeably--even with the Amaseis upgrade, I still find some significant
>advantages to using the two of them in this way.  To my knowledge, 
>Amaseis does not
>presently allow for saving (exporting) the spectral data, whereas 
>the version of
>WinQuake that I am using does.  I don't know if Larry has folded 
>that capability
>into the latest version of the code on his website.  The reason data export is
>valuable to me is because of the things I am able to do with the 
>data once I have
>loaded it into Excel.  For example, one can then generate phase 
>plots (numerically
>generated velocity versus position), correlation plots between two different
>records, etc, etc........ As much as I resist advertising Microsoft 
>products, Excel
>is in a class all its own!  Its use opens up a lot of new possibilities for a
>better understanding of seismology.  One thing that I regularly 
>compute with it are
>power spectral densities, for which (at least to the extent linear 
>assumptions are
>valid) the results are independent of the specifics of the instrument that
>collected the data.
>       What I see increasingly from the interchanges of this 
> listserve is impressive
>for the following reason--collectively we can advance seismology in 
>ways that may
>not even be possible for the professional science groups.  At least 
>in my career I
>have not observed comparable means to facilitate advancement.  The desire for
>knowledge, devoid of unwarranted arrogance, that I have seen in 
>listserve comments,
>is a refreshing change from most of my experiences over the last forty years.
>     Randall


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