contralto vs vocalizer

contralto and vocalizer both are nouns.

Word	Noun	Adjective	Verb	Adverb
contralto	Yes	Yes	No	No
vocalizer	Yes	No	No	No

As nouns, vocalizer is a hypernym of contralto; that is, vocalizer is a word with a broader meaning than contralto:

Other hypernyms of contralto include singer, vocaliser, vocalist.

contralto (noun)	vocalizer (noun)
the lowest female singing voice	a person who sings
a woman singer having a contralto voice	an organism that can utter vocal sounds

contralto (adjective)	vocalizer (adjective)
of or being the lowest female voice