As I understand it, digital hearing aids perform fourier transform (FFT) on the incoming sound signal from the microphone. The mic sampling frequency and the number of FFT points determine the frequency resolution of the hearing aid. For example, a hearing aid with 16000 Hz mic sampling frequency that performs a 64 point FFT would have 32 channels, with frequency resolution of 250 Hz. Number of FFT points is usually a power of two, so I can understand a hearing aid having 32 channels.

But what happens in a hearing aid with number of channels that are not a power of 2? I have seen on the website of some manufactures who say they have hearing aids from 4 to 24 channels, with recommended value being 12 channels, etc. How do they achieve these non-power-of-2 channels? For a hearing aid with 12-channels, is it internally actually a 16 channel hearing aid, and they just ignore the remaining 4 channels? Any ideas for understanding this would be highly appreciated.