Soprano or alto
I believe the answer is:
voice
I believe this clue is a double definition.
'soprano' is the first definition.
(thesaurus)
'alto' is the second definition.
(thesaurus)
(Other definitions for voice that I've seen before include "Spokesperson" , "Speak of - mouthpiece" , "Sound of speech" , "Sound produced in speaking" , "(Human) utterance" .)