Echoing effect (6)
I believe the answer is:
reverb
'echoing effect' is the definition.
(I've seen this before)
This is the entire clue.
(Other definitions for reverb that I've seen before include "Musical effect produced via an amplifier" , "Device causing a musical echo" , "(Device for producing) an artificial musical acoustic" , "Device creating artificial acoustics" , "Echo in music" .)