Settle argument using hard-core bit of speed (9)
I believe the answer is:
arbitrate
'settle argument' is the definition.
'arbitrate' can be an answer for 'settle' (arbitrating is a kind of settling). I am not certain of the 'argument' bit.
'hard-core bit of speed' is the wordplay.
'core' indicates the central letters.
'bit of speed' becomes 'bitrate' (I can't justify this - if you can you should believe this answer much more).
The central letters of 'hard' are 'ar'.
'ar'+'bitrate'='ARBITRATE'
'using' is the link.
Can you help me to learn more?
(Other definitions for arbitrate that I've seen before include "Mediate" , "Decide" , "judge" , "Act between disputing parties" , "Help settle a dispute" .)