soprano vs singing voice

soprano and singing voice both are nouns.

Word	Noun	Adjective	Verb	Adverb
soprano	Yes	Yes	No	No
singing voice	Yes	No	No	No

As nouns, singing voice is a hypernym of soprano; that is, singing voice is a word with a broader meaning than soprano:

soprano (noun)	singing voice (noun)
the pitch range of the highest female voice	the musical quality of the voice while singing
the highest female voice; the voice of a boy before puberty
a female singer with the highest vocal range of all the voice type

soprano (adjective)	singing voice (adjective)
having or denoting a high range