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From: zazula@uazhe0.physics.arizona.edu (RALPH ZAZULA)
Newsgroups: comp.sys.next
Subject: Help needed getting 4096 pt. FFT to work on DSP
Message-ID: <7MAR91221326@uazhe0.physics.arizona.edu>
Date: 8 Mar 91 03:13:26 GMT
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I'm trying to do a 4096 pt. FFT on the DSP using the program
/NextDeveloper/Examples/DSP/ArrayProcessing/fft/fft.c 
as a template.  All I did was to take out the test arrays, 
put in my own function for timeReal,timeImag and change POINTS.

A couple of interesting things are happening.  First, the signal
I'm putting in is two sine waves of different frequency in the timeReal
array and leaving timeImag all zeros.  I find that I have to scale the
timeReal array *way* down (the signal is sin(99)+sin(100) and I'm
dividing by 10).  I think this has to do with the fact that the DSP
uses numbers between 0-1 (right?).  

I can run this program for 1024 data-points.  2048 kills it (it just
sits there).  Is 2048 points too many for the data space of the DSP?
Could I reduce the size of the sinTab and cosTab arrays?  How can I
get up to 4096 data points?  (I'd like to take my 2048 points and 
zero pad out to 4096...).

Thanks,
Ralph


   |----------------------------------------------------------------------|
   | Ralph Zazula                               "Computer Addict!"        |
   | University of Arizona                 ---  Department of Physics     |
   |   UAZHEP::ZAZULA                            (DecNet/HEPNet)          |
   |   zazula@uazhe0.physics.arizona.edu         (Internet)               |
   |----------------------------------------------------------------------|
   |   "You can twist perceptions, reality won't budge."  - Neil Peart    |
   |----------------------------------------------------------------------|