PSN-L Email List Message

Subject: Re: Re[2]: FFT Waterfall display
From: "Geoffrey" gmvoeth@...........
Date: Sat, 14 Jul 2007 15:55:09 -0700

Hello Chris and PSN;

I believe everything you are telling me.
BUT, Real time is not really real time.
The speed can be tremendous and possibly
a sample rate of a megaherts and special whatever
will produce a spectrum line in record time.

BUT as a human looking at things you will
not see reality in your brain until you can
perceive it and that takes time.

What we call real time is possibly 100ms
behind real time.

To see real time you must see into the future
ahead of where you really are and since I do
not believe in time travel in the sci-fi sense
We as human beings are prisoners of only
the present minus the time it takes our souls
to realize it.

I myself do not need , Real Time, because I am not
looking for enemies like the military always does.

I only need to be able to analyze the data I produce
to understand a bit better about the reality that
surrounds me.

I can now see partly with this new FFT thing I have
put together with help from wherever that
I seem to understand my hardware somewhat
but most probably never completely.

I am searching for free knowledge to help me
use the current tools at my disposal to understand
better this seismic hobby and its related sciences.
I have no capitalistic intertests.
I am sick from fighting humanity.
The USA calls me mentally ill but I happen
to believe the sickness is really theirs.

Thanks for your response.
----- Original Message ----- 
To: ; 
Sent: Saturday, July 14, 2007 06:48
Subject: Re: Re[2]: FFT Waterfall display

> In a message dated 2007/07/14, gmvoeth@........... writes:
>> The power needed for a real-time FFT display of any value just does not 
>> exist for a typical home computer. You would need a special card like these high 
>> speed video cards.
>> I have seen the machines that do real time fft and back in the 1970s they 
>> were like 1000X faster than your home computer and would do 500 points and be 
>> only a few milli seconds behind real time. You most probably will have to 
>> stick with after the fact processing.
> Hi Geoff,
>       There have been several developments in FFTs since the 1970s!!
>       The amount of maths required to produce a FFT has been drastically 
> reduced by new algorithms.
>       The processors are now thousands of times faster, several may be 
> included on one chip and they can use vectored instructions.
>       It is largely a question of what you are calling 'real time'. 
>       If you use a multitasking processor, the interrupts are maybe 20 to a 
> few milliseconds or less. Such time delays are not usually important in 
> amateur seismology. The most likely delay is the relatively slow rate of seismic 
> sampling. By opting for a 10 Hz low pass filter, you are accepting a 50 milli 
> second delay minimum.
>       I would not expect there to be a problem in providing a FFT display to 
> update at this rate. I note quoted times of less than 1 milli second to 
> complete a FFT sample.
>       Regards,
>       Chris Chapman   

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