Thanks for your quick reply. Well, it seems wpfsvl is a good way to go, but I have 2 problems now:
1) Wpfsvl needs .Net Framework 4.0 and I don´t want to have to install it on my computers.
2) There is a example project showing the usage of NAudio with it, but source code or guides for the compiled NAudio example are not provided :-Y . That makes me angry, it wouldn´t be that much work to include the example project source code ...
=> So this seems to be a dead end. Could you please release an example of using FFT with NAudio? Would be fantastic!! I would be your biggest fan then :) It should only show the basic functions, I don´t need a full example. I don´t want to steal your spare time you know :)