Grumpy_Mike:
Well I think this project is beyond you at the present time. One problem with beginners these days is that they tend to take on too much too soon without learning the basics.Have you tried googling FFT? It is some very advanced math that you will not encounter until you are 19 at least. Even then when you understand it you will find it does not do what you want and you will find it hard to get the correct octiave out of it.
I would suggest getting an electronic tuner as that will be far cheaper than what to can do with an Arduino.
Thank you..
I just thought of an idea and wanted to know how it would work.
I'm not sure whether I'll make it or not..