mid vowel vs vowel sound

mid vowel and vowel sound both are nouns.

Word	Noun	Adjective	Verb	Adverb
mid vowel	Yes	No	No	No
vowel sound	Yes	No	No	No

As nouns, vowel sound is a hypernym of mid vowel; that is, vowel sound is a word with a broader meaning than mid vowel:

mid vowel: (linguistics) Any vowel sound made with a somewhat elevated position of some certain part of the tongue, in relation to the palate; midway between the high and the low.
vowel sound: a speech sound made with the vocal tract open

Other hypernyms of mid vowel include vowel.

mid vowel (noun)	vowel sound (noun)
(linguistics) Any vowel sound made with a somewhat elevated position of some certain part of the tongue, in relation to the palate; midway between the high and the low.	a speech sound made with the vocal tract open