Programmatically 'Listening' to Sound (Signal Processing?)

Question

I\'m familiar with Computer Vision (Well, know OF it), of which one application can be image recognition, such as Optical Character Recognition, I believe. However,

Answer 1

I remember a while ago I saw a preview of an application (Sorry, forgot the name) which could listen to a recording of someone playing a guitar, and automatically graph it out across a time-line with the actual notes/chords that were played.

You might also be thinking of Melodyne: http://www.celemony.com/cms/

Though Vari audio in newer version of Cubase is pretty similar. :)