Working on pitches in this discipline? (9)
I believe the answer is:
phonetics
'this discipline?' is the definition.
(phonetics is a kind of discipline)
'working on pitches' is the wordplay.
'working' indicates an anagram.
'on'+'pitches'='onpitches'
'onpitches' is an anagram of 'PHONETICS'.
'in' is the link.
(Other definitions for phonetics that I've seen before include "Study of speech sounds" , "Science of speech sounds" , "Branch of knowledge concerned with speech sounds" .)