The runfftlistener programm is made to illustrate how you can use the FFT package of the library. The goal is to determine the frequency of the sound comming from the microphone number 0. If the frequency is under 900Hz the e-puck will turn left. If the frequency is between 900Hz and 1800Hz the e-puck will go forward. If the frequency is over 1800Hz the e-puck will turn right.