Composer put in octave nervously (7)
I believe the answer is:
tavener
'composer' is the definition.
(Sir John Kenneth Tavener 1944-2013, composer)
'in octave nervously' is the wordplay.
'in' indicates a hidden word.
'TAVENER' is hidden in the letters of 'octave nervously'.
'put' acts as a link.
(Other definitions for tavener that I've seen before include "Modern composer, John (not the 16th century one)" , "One in a bar" , "British composer, b. 1944 (not the 16th century one)" .)