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question about the result of fft

Jogging Song
Intellectual 685 points

Hi,all
    I'm using fft functions from dsplibrary_v210. For the function DSP_fft16,
the result is significantly different from the result generated by matlab.
Minor difference is acceptable because of computation precision.
In the document spra884a, it mentions that input data is scaled for preventing
overflow. In my case input data is small,just integer from 0 to 31 for
a 16 point FFT. The same is with DSP_fft16r. But DSP_fft16x32 works well.

Best Regards
Jogging

  • 0
    Intellectual 685 points

    Hi,all
       In the document sprue8b, it says that All stages except
    the last one scale by two the stage output data.  Does it mean that
    I need to right shift the result to botain correct result?

       It also says that All data are in short precision or Q.15 format.
    What does it mean? The data must be in the range of (-1,1)?

      Is the document spra884a outdated? I don't find a updated one available?
    Best Regards
    Jogging

  • 0 in reply to Jogging Song
    Prodigy 100 points

    Hi，Jogging

         I have the same question with you ,  the result of DSP_fft16x16  is different from the matlab'results .In matlab' result  I found some output data is very big and overflowed the 16 bits.You said  DSP_fft16x32 works well? I will test it . My english is poor.Sorry...

        And how can you modify the example for the dsplib ? Are you use the linux enviroment ? Where can I modify the example to fit the dsplib ?I put the fft source code (DSP_fft16x16_i )together now and I compile  them .How can I use the asm source code .

       Thanks.

    Best Regards

    Tiny