Voice changed a lot (4)
I believe the answer is:
alto
'voice' is the definition.
(alto is a kind of voice)
'changed a lot' is the wordplay.
'changed' indicates anagramming the letters.
'a'+'lot'='alot'
'alot' is an anagram of 'ALTO'.
(Other definitions for alto that I've seen before include "The highest adult male singing voice" , "Singing voice between tenor and soprano" , "Member of choir" , "High male singing voice" , "Woman's singing voice" .)