Using the diff function to identify notes in a tune.

I have a wav file (A monophonic recording of 'Iron man' by Black Sabbath just fyi ;) ). when i differentiate the recording i can see prominent spikes in the graph plot of it, that show where a new note is played, from here i need a way to isolate these notes and save them all in my workspace. At this point frequency of notes is not needed, simply recognising isolating unique notes.

How do i take the results of 'diff' and make it into usefull data? Find peaks doesnt seem a solid way to do it because of pottential noise spikes in the data.

thanks