Tool REM deployed for musical effect (7)
I believe the answer is:
tremolo
'musical effect' is the definition.
(I've seen this before)
'tool rem deployed' is the wordplay.
'deployed' is an anagram indicator.
'tool'+'rem'='toolrem'
'toolrem' is an anagram of 'TREMOLO'.
'for' is the link.
(Other definitions for tremolo that I've seen before include "Violin's rapid repetition of a single note" , "Paganini's effect" , "Wavering note" , "Shaky effect in music" , "Vibrato effect" .)