Echoing note resounding initially — with this? (6)
I believe the answer is:
reverb
'this?' is the definition.
I don't know anything about this answer so I cannot judge whether this works.
'echoing note resounding initially' is the wordplay.
'echoing' says the letters should be written backwards (echo can mean to reflect or bounce back).
'note' becomes 'breve' (musical note).
'resounding initially' becomes 'r' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'breve'+'r'='brever'
'brever' backwards is 'REVERB'.
'with' acts as a link.
Can you help me to learn more?
(Other definitions for reverb that I've seen before include "Echoing effect" , "Device causing a musical echo" , "Musical device producing echoes" , "Electronic effect added to music" , "music made by this device" .)