A modulation of voice in which to make reparation (5)
I believe the answer is:
atone
'to make reparation' is the definition.
(thesaurus)
'a modulation' is the wordplay.
'modulation' becomes 'tone' (I've seen this in another clue).
'a'+'tone'='ATONE'
'of voice in which' is the link.
I am not very happy about this link. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for atone that I've seen before include "In agreement - sounds singular" , "Make up for wrong done" , "Expiate" , "Make reparation for a misdeed" , "remedy" .)