Composing short creation in arrangement (13)
I believe the answer is:
orchestration
'composing' is the definition.
(I know that orchestration is a type of arrangement)
'short creation in arrangement' is the wordplay.
'in arrangement' indicates an anagram (I've seen this in other clues).
'short'+'creation'='shortcreation'
'shortcreation' anagrammed gives 'ORCHESTRATION'.
(Other definitions for orchestration that I've seen before include "Arrangement for instruments - short reaction (anag)" , "Arrangement of string, brass, woodwind and percussion parts" , "Musical arrangement" , "Composer's skill" , "Note arrangement" .)