All 4 Uses

audible
in
Roll of Thunder, Hear My Cry
(Edited)

Wide eyes turned to the covered teacher's platform directly in front of them and an audible sigh of relief swelled in the room.
p. 22.4

audible = able to be heard
He sulked for a while with a few audible grumbles which no one paid any attention to, but finally he fell asleep and did not awaken until we had driven up the Granger road and stopped in front of the Avery house.
p. 117.4
Stacey's voice faded into an inaudible whisper as Mama slowly put the sewing box on the table behind her.
p. 141.8

inaudible = unable to be heard

standard prefix: The prefix "in-" in inaudible means not and reverses the meaning of audible. This is the same pattern you see in words like invisible, incomplete, and insecure.
"What did Mr. Jamison want?" she asked, her voice barely audible.
p. 200.3 *

audible = able to be heard

Definitions:

(1) (audible as in: barely audible)
capable of being heard
(2) (meaning too rare to warrant focus)
In football, the term has come to include an instruction shouted from the line of scrimmage.

Recently, the word is also being used to indicate sounds that could be played on a phone or computer; for example "audibles include creative hellos that can be downloaded."