I have planned with arduino frequenzen to compare, in which I take a frequency, save and then compare with a second recording.
I've already heard of the fft library, but I cannot handle with her.
My problem is that I do not know how I can calculate the frequency with the input from the microphone.
I hope someone can help me.
Look at this project, its listening , store and compare voice password.
http://coolarduino.wordpress.com/2012/01/