A group of notes, we hear, producing harmony (6)
I believe the answer is:
accord
'harmony' is the definition.
(accord is a kind of harmony)
'a group of notes we hear' is the wordplay.
I cannot really see how this works, but
'a' is found in the answer.
'of' could be 'o' and 'o' is present in the answer.
'notes' could be 'cc' (two C's - as in the musical note C) and 'cc' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'producing' acts as a link.
Can you help me to learn more?
(Other definitions for accord that I've seen before include "Model" , "'Agreement, treaty (6)'" , "Official treaty" , "Harmony, concurrence" , "Match" .)