Voice changing a lot (4)
I believe the answer is:
alto
'voice' is the definition.
(alto is a kind of voice)
'changing a lot' is the wordplay.
'changing' indicates an anagram.
'a'+'lot'='alot'
'alot' anagrammed gives 'ALTO'.
(Other definitions for alto that I've seen before include "Kind of singing voice, male or female" , "Counter-tenor or contralto" , "someone to sing" , "One who sings" , "Unisex vocal range" .)