I have been reading quite a bit about FFTs and I understand quite well the following:
- radix 2 FFT, and its 'divide and conquer' advantage vs DFT,
- radix 4 FFT, and why it is better than radix 2 FFT (1 radix 4 needs an overall lower number of operations than 2 radix 2 FFTs),
- split radix 4/2 FFT: 'naively' it looks like there are more operations than radix 4, but actually quite a few more trivial operations (in particular multiplications by
-ithat actually need no complex multiplications), so less 'expensive' operations overall.
My question is: I cannot find as much / I read much less about 'higher radix' FFTs: I can find a bit here and there about radix 8, very little about radix 16, nothing so far about radix 32, 64, and
2**n in general. Naively, I would have guessed that going for higher and higher
2**n radix for array length that are compatible with it should give additional gains compared with combining several lower radix stages. Is this wrong / any reason why higher radix FFTs are not discussed as much?