Suggestions for FFT based tools to analyze music - Preferably MATLAB/free software packages I am interested in analyzing full length songs for general features of the track which are not otherwise apparent. For e.g., I want to look at various parts of the song with time-frequency plots/wavelets/other signal processing tools for, lets say -  How does the frequency content of the song during the guitar solo compare to the part when only vocals are on? What is the frequency with which the guitar solo starts? What is its peak? ..and so forth.

Although I use FFT often for research, this is something I am fascinated by.... Any suggestions where to start?

At this point I have got WAV files for MATLAB analysis, since they have almost no loss. Where do I go from here? Any references to concepts/open source codes/literature etc. would be greatly appreciated. 

Also, I am not into audio engineering or anything similar. Its just for my own interest.
My favorite is Sonic Visualiser. It is free and fast. In combination with the Vamp Plugins you can analyze low level features up to high level features like onsets, pitches, chords and so on. It has also an nice spectrum and spectrogram fea