singing voice vs vocalism

singing voice and vocalism both are nouns.

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

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

singing voice: the musical quality of the voice while singing
vocalism: the sound made by the vibration of vocal folds modified by the resonance of the vocal tract

Other hypernyms of singing voice include phonation, vocalisation, vocalization, voice, vox.

singing voice (noun)	vocalism (noun)
the musical quality of the voice while singing	the sound made by the vibration of vocal folds modified by the resonance of the vocal tract
	the system of vowels used in a particular language