Piece of music -- turn it on, oddly (4)
I believe the answer is:
trio
'piece of music' is the definition.
(trio is a kind of piece of music)
'turn it on oddly' is the wordplay.
'oddly' indicates alternate letters.
'turn'+'it'+'on'='turniton'
The alternating letters of 'turniton' are 'TRIO'.
(Other definitions for trio that I've seen before include "Three together" , "Chamber group" , "Riot (anag)" , "Small group playing" , "A group or set of three" .)