Synthesis DFT Filter Bank I have a DFT bank analyzer with N channels, but the the bandwidth of the signal occupies only the first 2 channels, therefore I'll reconstruct only these and not entire full bandwidth. I'd like to know if is mandatory to use an FFT with N points all polyphase components in the synthesis bank and . I would to use only FFT 2 points and only 2 polyphase components(8 taps each) in the synthesis bank. Is it possible?

Thanks to all
Stefano
Any spectrum that is between the two DFT bin centers ends up getting represented, in various proportions, in all the DFT bins (in the rectangular window case, the proportions decay as in a Sinc function, roughly by 1/(i-k)).  Those proportions might be needed for your synthesis to be an accurate enough reconstruction.

Using 2 bins alone usually creates a beating effect at a low beat frequency.