Dobly Digital 5:1 (also known as AC-3) is an audio encoding process that gives the listener the illusion of total surround sound. AC-3 consists of five speakers and one bass unit (hence the name 5:1). Referring to figure 1 (not drawn to scale) on the right, the listener is surrounded by two front speakers and two rear speakers, both pair of speakers with full stereo capabilities. The center speaker is mainly used for dialogue between actors and actresses.

Because both the front and rear speakers are stereo, AC-3 is able to simulate the movement of objects (such as a shot fired) from back to front and vice versa. For example, sound may be encoded so that the sound begins from the rear right speaker and travel to the front left speaker.

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