Melody’s strain (4)
I believe the answer is:
tune
I believe this is a double definition.
'melody's' is the first definition.
(synonyms)
'strain' is the second definition.
(synonyms)
(Other definitions for tune that I've seen before include "Of engine, adjust to run smoothly" , "temper" , "Optimise the condition of" , "Improve quality" , "Adjust (car engine); air" .)