Fast Fourier Transform filtering is certainly an option. It's a very intuitive solution since, like BobJanova states, band-pass filtering can be easily achieved by doing these steps: 1) Forward FFT of the input data, 2) Zeroing the result bins of the frequencies that we want to remove, and finally, 3) Perform reverse FFT on the same data. However, this is a very expensive approach, if fast execution is a must, I would recommend trying a FIR digital filter instead. I have no experience designing such a filter myself, but there used to be a really great freeware tool around named DSPlay. I Googled for a while and unfortunately can't find it any more. This GUI tool allowed you to easily create band-pass filters by specifying a few input parameters and generated very simple C code that was directly usable in C#. Let me take a look as I'm certain I have the DSPlay tool in a pervious hard disk backup... :)
