(
Active
Coding-
3) Dolby's third digital audio coding technology based on a perceptual coding method. Introduced in 1991 initially for surround sound in theaters, AC-3 is more advanced than AC-2 and provides six channels of audio in less space than a two-channel stereo CD. AC-3 and "Dolby Digital" are synonymous. See
Dolby Digital,
AC-1 and
AC-2.