subvocalise vs sound out

subvocalise and sound out both are verbs.

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

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

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

subvocalise (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