Is it ensure, insure, or assure?
"sound," especially recorded or transmitted, 1934, abstracted from prefix audio- (in audio-frequency, 1919, etc.), from Latin audire "hear" (see audience).
word-forming element meaning "sound, hearing," from comb. form of Latin audire "hear," (see audience); first used in English as a word-formation element 1913.
file format Sound, one component of multimedia. Computers (and audio compact discs and digital audio tape) work with digital audio, in contrast to vinyl disks or analogue tape. (1999-07-30)