subvocalize vs sound out

subvocalize and sound out both are verbs.

Word	Noun	Adjective	Verb	Adverb
subvocalize	No	No	Yes	No
sound out	No	No	Yes	No

As verbs, sound out is a hypernym of subvocalize; that is, sound out is a word with a broader meaning than subvocalize:

Other hypernyms of subvocalize include articulate, enounce, enunciate, pronounce, say.

subvocalize (verb)	sound out (verb)
articulate without making audible sounds	try to learn someone's opinions and intentions
	speak, pronounce, or utter in a certain way