tone down vs soften

tone down and soften both are verbs.

Word	Noun	Adjective	Verb	Adverb
tone down	No	No	Yes	No
soften	No	No	Yes	No

As verbs, soften is a hypernym of tone down; that is, soften is a word with a broader meaning than tone down:

tone down (verb)	soften (verb)
make less strong or intense; soften	become soft or softer
deaden (a sound or noise), especially by wrapping	make soft or softer
	lessen in force or effect
	make less severe or harsh
	protect from impact
	make (images or sounds) soft or softer
	give in, as to influence or pressure