ablaut vs vowel sound

ablaut and vowel sound both are nouns.

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

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

ablaut: a vowel whose quality or length is changed to indicate linguistic distinctions (such as sing sang sung song)
vowel sound: a speech sound made with the vocal tract open

Other hypernyms of ablaut include vowel.

ablaut (noun)	vowel sound (noun)
a vowel whose quality or length is changed to indicate linguistic distinctions (such as sing sang sung song)	a speech sound made with the vocal tract open