Vibrating vocal effect (7)
I believe the answer is:
tremolo
'vibrating vocal effect' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for tremolo that I've seen before include "Fluctuation in pitch" , "A vibrating effect in music" , "Vibrating musical effect" , "Musically shivering" , "Unsteady effect" .)