PSN-L Email List Message

Subject: Re: Most Recent Discover Magazine pp66-67 WaterFall Display
From: Mike Price mprice@........
Date: Sun, 08 Jul 2007 11:39:07 -0700

The FFT algorithm is well documented and implementations abound. The FFT 
is widely used by anyone interested in exploring data in the frequency 
domain and it would be hard to find an algorithm better explained or 
more readily available. A Google search for "fft source code" generates 
1.3M hits; indeed, the first one is which has downloadable 
C source and links to many other sites containing source in several 
languages. You can find a basic implementation at: for example.

The notion that access to FFT code is somehow restricted is misguided.


Geoffrey wrote:
> This program seems to not use data files
> but wants you to build a custom A/D that
> will be read by the program itself.
> Not sure a sound card will take sample rates
> as low as 20Hz because most sound hardware
> has a capacitor input that rejects DC or freqs
> below the sense of hearing.
> It would be so nice to have this feature in Winquake to
> do an Analysis of file data in TXT/8/12/16/24 bit form
> or text form all you have to do is limit the frq
> between Dc and 5 Hz or so and make atleast
> 1024 samples per spectrum line.
> I have seen the routine in the library at ASU
> to FFT and there seems to be several ways.
> The best i like seems to result in the final
> results with the number of samples to be worked
> setting the resolution over the band.
> These people who write these books on FFT are oriented
> only to their own kind so if you do not know calculus or higher
> transforming their ideas into a computer program is very difficult.
> But I have in the past done this successfully myself.
> On a very small scale with a VIC20 machine running 10MHz.
> You need to take the first 1024 samples then make an imaginary
> set from the same ones then do a butterfly operation
> (some kind of fancy math) that results in a backward
> spectrum with each sample now representing a frequency band.
> Then you straighten out the results to get the low freq at the low
> sample number position.
> The final results is the freq range represented within the sample set 
> chosen
> and that would be line one.
> Then you advance one sample in the data and do the same for the
> next contiguous 1024 samples.
> This is repeated until you have built a picture of your entire data file.
> The sample rate determins the freq limits I think.
> Why do not more people take an interest
> in the math and programming and hardware
> because seismology is just a fine specialty
> and I think more serious PROs should take an
> interest in fostering human interests in all lines of Science.
> You got to be an MD or equiv before you can
> get into forensic medicine ot Toxicology but this
> Seismology stuff is non license stuff and great way to
> learn many facets of science.
> Please someone with Math background make us a
> Basic Program like QBASIC or POWERBASIC
> to do one line of FFT and I will take it from there
> to make the whole program.
> I did this once myself but did not record the final
> program and would have to learn everything all over
> again to do this program again.
> A Burgler stole the VIC20 laptop with all my programs
> several years ago so those programs are lost.
> There is more to amateur stuff then just watching the waves
> and building things with your hands. It is a great chance
> to play general science and bring most everything together
> to see how it works with NO MYSTRIES.
> There seems to be effort to compartmentize information
> in the USA because of its capitalistic nature forcing one
> to become a college goon before you are able to
> do anything academic. The truth of the matter
> is to get a formal degree the system studies you as much
> as you study your subject so there is no real privacy
> or artisic freedom for the adventerous academic without
> government awareness. The Counter Intelligence peoples
> do not want Academic Freedom in the USA.
> Even tho we are playing with this harmless passive seismology stuff.
> I have come to realize that in some European Countries
> they have laws amounting to NEPLEONIC LAW which basically
> says everything is illegal except that which is specified by government.
> These kinds of forces are what we up against even in this
> relatively harmless area of seismology.
> If there is no common place to get knowledge we must make it ourselves
> even if it angers the powers that be.
> It is no accident we can not find a simple BASIC FFT source code
> with logic trees etc in laymen terms for our interest area.
> Everyone is trying to keep secrets or make money.
> For the sake of the evolution of science lets
> please gather together a collection of utility programs
> free for universal use in this PSN group.
> I am assuming PSN means Public like WORLD PUBLIC and not just
> California Public.
> One LAST thing for NOW.
> Black and White and shades of gray is by far the best for resolution 
> and universal readability.
> If a person is lucky to get a totally black and white monitor or green
> you will see no sharper images than with such an analog electrostatic 
> scanning device.
> The military used to preferr these over color since it used to be all 
> male
> (for warships)
> and males have the highest incident of color blindness.
> Regards;
> geoff
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