So, as you advised me, i did some research and i understand a little bit more about audio input into arduino circuit.
I understand better what @Grumpy_Mike said about the pull up pull down resistor and the capacitor in order to DC Offset the signal.
i've also read somewhere that i should use an amplifier (a non inverting amplifier) in order to get a 5v signal. Do you confirm that ?
I guess it might be a bit difficult for me to work on this code but i'm confident i'll end up with something good