PSN-L Email List Message

Subject: FFT BASIC Source Code
From: "Geoffrey" gmvoeth@...........
Date: Sun, 8 Jul 2007 12:41:22 -0700

Hello PSN;

I found my very old notes from ASU Nobel Science Library regarding
FFT basic program and I think it shows
the source material it was found in.

Can someone who understands FFT please look at this
and comment to me at my address gmvoeth@........... or to PSN or to Both.

I intend to make a DOS executable program to use
8 bit data that will display the results in 640X480X256 if at all possible. I will share my results if things look good.

The only question I have is that about real and imaginary.

I assume real means sine of the data and imaginary means cosine of the data
and the angle relates to the sample rate vs the desired frequency and summed acxcording to the sample number and that the complete 
butterfly operation needs
to be done 1024 times for each desired freq to look at.
The bandwidth of each freq will be related to the number of samples processed. What I do not understand is how
can you measure frequency unless you start out in phase
with the freq you are looking for ??

Basic Source code for the FFT is very hard to find.

Out of that whole library in the 1980s this is the only basic example I found.

Maybe one of you experts can tell me if this program is honestly workable
and the results will be proper ?

I understand to save space you can use
the same memory locations as the original data
to put the results into but it (results) will be reversed
and you need to start your freq display using the highest
result (N) as the lowest Frq in the display (N).

This computation although it is called FFT is very
labor intensive and the time will increase exponentially
to get the results according to the number of samples
you process each line.

If Im not mistaken it took me several minutes with the 10MHz VIC20 chip CPU
to complete a single spectrum line using only 1024 samples.
Today my machine is P4 3GHz so I should expect seconds instead of minutes.




Public Seismic Network Mailing List (PSN-L)

[ Top ] [ Back ] [ Home Page ]