talking book vs audio

talking book and audio both are nouns.

Word	Noun	Adjective	Verb	Adverb
talking book	Yes	No	No	No
audio	Yes	No	No	No

As nouns, audio is a hypernym of talking book; that is, audio is a word with a broader meaning than talking book:

talking book: sound recording of someone reading a book; frequently used by blind people
audio: a recording of acoustic signals

Other hypernyms of talking book include audio recording, sound recording.

talking book (noun)	audio (noun)
sound recording of someone reading a book; frequently used by blind people	the sound elements of television
	a recording of acoustic signals
	an audible acoustic wave frequency
	the audible part of a transmitted signal