Notice only signified sound tuning (10)
I believe the answer is:
adjustment
'tuning' is the definition.
(thesaurus)
'notice only signified sound' is the wordplay.
'notice only' becomes 'adjust' (I can't justify this - if you can you should give a lot more credence to this answer).
'signified' becomes 'meant' ('mean' can be a synonym of 'signify').
'sound' indicates a 'sounds like' (homophone) clue.
'meant' sounds like 'ment'.
'adjust'+'ment'='ADJUSTMENT'
Can you help me to learn more?
(Other definitions for adjustment that I've seen before include "Ordering" , "Minor modification" , "Adaptation" , "Small change to achieve a desired result" , "Fitting" .)