Pulsating effect in instrumental or vocal tone (7)
I believe the answer is:
vibrato
'pulsating effect in instrumental or vocal tone' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for vibrato that I've seen before include "Singing effect" , "Pulsating effect in instrumental or vocal tone" , "Rapid pitch variation" , "Rapid alternation in pitch" , "Oscillatory effect" .)