Raised note beginning to reinforce echo effect (6)
I believe the answer is:
reverb
'echo effect' is the definition.
(I've seen this in another clue)
'raised note beginning to reinforce' is the wordplay.
'raised' shows that the letters should be reversed in order (going up in a down clue).
'note' becomes 'breve' (musical note).
'beginning to' indicates taking the first letters.
The first letter of 'reinforce' is 'r'.
'breve'+'r'='brever'
'brever' reversed gives 'REVERB'.
(Other definitions for reverb that I've seen before include "Echoing device" , "Effect where amplified sound vibrates" , "What can change our perception" , "Musical device producing echoes" , "Device causing a musical echo" .)