I learned a huge amount from one friend who is musical, just by listening to him describing his experience.
"Firstly I hear the flavour of the note, and then I figure out the range -- which octave it is in"
(he has perfect pitch)
"Right now the music is screaming out G MAJOR to me"
"...the bottom of the scale"
(where I would have expected him to say "the tonal centre")
From simple expressions such as these, I start to get some idea of how his mind works musically, and this is valuable understanding.
Are there any well-known examples of musicians attempting to translate their experience into language?