Notation for drums with true transposition (9)
I believe the answer is:
tablature
'notation' is the definition.
(tablature is a kind of notation)
'drums with true transposition' is the wordplay.
'drums' becomes 'tabla' (I've seen this before).
'with' is a charade indicator (letters next to each other).
'transposition' indicates anagramming the letters.
'true' with letters rearranged gives 'ture'.
'tabla'+'ture'='TABLATURE'
'for' is the link.
(Other definitions for tablature that I've seen before include "musical notation" , "Form of music notation" , "Guide to fingering" .)