Re: Very large FFT

Yes it is clear to me that this is the same Twiddle array that I previous
calculated that for increasing the speed of the FFT calc, but why is he
making it then again ?

It looks like
- FFT with twiddle
-Twiddle again (???)
- FFT with twiddle
-final answer

I noticed the same in a PhD thesis on radio astronomy in the appendix C
where the author made an extra Twiddle step. In the referenced
presentation from Dillon Engineering there was also this step.

What is the purpose of it? Is the 1D FFT calculated as 2D matrix really
that much different to the image processing 2D FFT ?


Without it you don't get a 1M FFT when you are done. It would be nice
not to have to do it, but if you don't do the extra twiddle multiply
you would have a 2D FFT 1k x 1k FFT and not a 1M FFT.

Tom

.

Relevant Pages

  • Re: Twiddle factor table creation for FFT generation
    ... of multiplications & additions) in finding the ... FFT ... one reason that i mentioned generating the twiddles in bit-reverse ... order is because of the accumulated error one gets each time a twiddle ...
    (comp.dsp)
  • Re: Twiddle factor table creation for FFT generation
    ... robert bristow-johnson wrote: ... twiddle factors are the greatest source of errors in the FFT ... Schatzman, Accuracy of the DFT and the FFT, SIAM J. Sci. ... Schatzman's results are for the recursion used in FFTPAK. ...
    (comp.dsp)
  • Re: FFT twiddle calculation and evaluation
    ... I am aware that for a DIF radix-2 FFT the total number of butterflies is ... Also the last stage involves multiplication by a twiddle ... Lyons, R. "Program Aids Analysis of FFT Algorithms", ...
    (comp.dsp)
  • Re: Phase/twiddle factors calculations
    ... I am aware that for a DIF radix-2 FFT the total number of butterflies is ... the last stage involves multiplication by a twiddle factor of 1. ... Lyons, R. "Program Aids Analysis of FFT Algorithms", ...
    (comp.dsp)
  • Re: Very large FFT
    ... Yes it is clear to me that this is the same Twiddle array that I previous ... FFT with twiddle ... where the author made an extra Twiddle step. ... presentation from Dillon Engineering there was also this step. ...
    (comp.dsp)