FFT_verification

[Altera_Forum]

Hi ! 

 When I run FFT and IFFT tool in megawizard, the results are not logical. For example firstly I run the FFT tool with the megawizard tb (input: natural order, output : digit reversed order) then I use the FFT output txt files for the input files of IFFT ( input : digit reversed order output: natural order) the result of IFFT dont match with the input of FFT . What could be the problem ?  P.S = I use single precision floating point representation for the 16-FFT tool.   Thanks all

[Altera_Forum]

Have you tried checking what the input file looks like when you generate a testbench for the IFFT, there's no guarantee the output file of the FFT matches the input format for the IFFT.

[Altera_Forum]

I used the output of FFT for the input of IFFT.I mean I modified the tb for IFFT. 

 By the way I found the solution ;) When you check in binary for floating point it is hard to find what is wrong.  When I converted to decimals in Matlab I saw that the output multiplied with the FFT size. For example if you use 8-IFFT the outputs are 8 time greater than the outputs had used to be. You should normalize them by IFFT size ;)  Thanks anyway for your reply

[Altera_Forum]

Hi ferdiskaras, 

 I guess I have the same problem you went through. I have implemented a VARIABLE STREAMING (N=8), SINGLE-FLOAT-POINT FFT/IFFT. These are my results:  input (natural order): (8 0 0 0 8 0 0 0)  FFT  output (Digit-reverse order): [16 16 0 0 16 16 0 0] /* the same as [16 0 16 0 16 0 16 0 ] Natural order */  input(Digit-reverse order): [16 16 0 0 16 16 0 0]  IFFT output (natural order): (64 0 0 0 64 0 0 0)  How did you normalize it? Where did you make de division by N? In your hardware or in your software? Is there a way to set FFT core to output data already normalized?  Thanks

[Altera_Forum]

If change the "I/O Output Order" of FFT and "I/O input order" of IFFT to "digital reverse Order", then the input of FFT should be equal to output of iFFT. I'm able to get the correct result.