Singer into special tonality (4)
I believe the answer is:
alto
'singer' is the definition.
(type of singing voice)
'into special tonality' is the wordplay.
'into' says the answer is hidden in the clue.
'ALTO' is hidden in the letters of 'special tonality'.
(Other definitions for alto that I've seen before include "Kind of singing voice, male or female" , "Low female singing voice" , "Voice part" , "Singing voice between tenor and soprano" , "The highest adult male singing-voice" .)