Surprisingly elitist rant by conservatoire's principal player (12)
I believe the answer is:
clarinettist
'player' is the definition.
(clarinettist is a kind of player)
'surprisingly elitist rant by conservatoire's principal' is the wordplay.
'surprisingly' indicates anagramming the letters.
'by' means one lot of letters go next to another.
'principal' says to take the initial letters.
The first letter of 'conservatoire' is 'c'.
'elitist'+'rant'='elitistrant'
'elitistrant' with letters rearranged gives 'larinettist'.
'larinettist' put after 'c' is 'CLARINETTIST'.
(Other definitions for clarinettist that I've seen before include "Musician, like Benny Goodman, say" , "Cats in litter (anag) -- woodwind player" .)