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From: srf@claudius.juliet.ll.mit.edu ( Steve Feinstein)
Newsgroups: comp.dsp
Subject: Re: Check of an FFT routine...
Message-ID: <SRF.91Apr4100830@claudius.juliet.ll.mit.edu>
Date: 4 Apr 91 15:08:30 GMT
References: <1991Apr4.004750.15969@en.ecn.purdue.edu>
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In-Reply-To: jbs@en.ecn.purdue.edu's message of 4 Apr 91 00:47:50 GMT

In article <1991Apr4.004750.15969@en.ecn.purdue.edu> jbs@en.ecn.purdue.edu (Spaggie) writes:
>   I have put together a program to do an FFT of any array of
>   data, but it doesn't seem to get the imag. part correct.
>   Can someone verify if this data is correct or not?
>
>
>                       my fft routine then yeilds th
>   Data given          Real, Imaginary              
>   -----------	        -------------------          
>   -0.005093	        -0.000200,-0.000000          
>   -0.003797	        -0.000201,-0.000001          
>   -0.001432	        -0.000212,0.000010           
>   0.004374	        -0.000223,-0.000053          
>   0.001606	        -0.000722,-0.000263          
>   0.000027	        0.000427,0.000433            
>   -0.004548	        -0.001282,-0.000314          
>   0.000919	        0.000184,0.001059            
>   0.005288	        0.000162,0.000016            
>   -0.004973	        0.000187,0.000170            
>   -0.001283	        -0.000096,-0.000125          
>   -0.001970	        -0.000621,0.000399           
>   0.002802	        0.000027,0.000028            
>   0.007448	        0.000258,-0.000585           
>   -0.000214	        -0.000188,-0.000254          
>   -0.006771	        -0.000111,0.000147           
>   -0.004697
>   0.002116
>   0.003964
>   0.002788
>   -0.000533
>   -0.003011
>   -0.000788
>   0.000005
>   -0.000852
>   0.003107
>   -0.001298
>   -0.000009
>   0.001896
>   -0.002197
>   0.000841
>   -0.000112
>	   Can anyone verify this as being correct?

Your values are wrong and there aren't enough of them, either.
You should be generating at least N FFT points for an N-point
array.  The example you've posted is a 16-pt FFT on 32-pt
data.  Here is what MATLAB generated:

  -0.0023  		-pi
  -0.0035 - 0.0047i
  -0.0060 + 0.0081i
   0.0083 + 0.0187i
   0.0009 - 0.0009i
  -0.0199 - 0.0128i
  -0.0031 + 0.0040i
   0.0060 - 0.0055i
   0.0052 - 0.0005i
   0.0059 - 0.0339i
  -0.0410 + 0.0101i
   0.0137 - 0.0138i
  -0.0231 + 0.0084i
  -0.0071 + 0.0017i
  -0.0068 - 0.0003i
  -0.0064 + 0.0000i
  -0.0064		0
  -0.0064 - 0.0000i
  -0.0068 + 0.0003i
  -0.0071 - 0.0017i
  -0.0231 - 0.0084i
   0.0137 + 0.0138i
  -0.0410 - 0.0101i
   0.0059 + 0.0339i
   0.0052 + 0.0005i
   0.0060 + 0.0055i
  -0.0031 - 0.0040i
  -0.0199 + 0.0128i
   0.0009 + 0.0009i
   0.0083 - 0.0187i
  -0.0060 - 0.0081i
  -0.0035 + 0.0047i	+pi


--

		Steve Feinstein

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