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Overview of Dolby Technologies 5. Consumer Surround Sound
Home theater system with four-channel Dolby Pro Logic playback.
Home theater system with four-channel Dolby Pro Logic playback.
Also see: Dolby Headphone: What's in it for you? (also PDF: 785KB)
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Dolby Surround is the consumer version of the original analog Dolby multichannel film sound format. When a Dolby Surround soundtrack is produced, four channels of audio information-left, center, right, and surround-are matrix-encoded onto two audio tracks. These two tracks are then carried on stereo program sources such as videotapes and TV broadcasts into the home, where they can be decoded to recreate the original four channels and the surround sound experience. Thousands of feature films on home video, as well as many television shows, are encoded in Dolby Surround.
Dolby Surround Pro Logic is the technology that decodes program material encoded in Dolby Surround; it is built into virtually every home theater audio system. Like the professional decoder units used in cinemas, Dolby Surround Pro Logic reconstructs the original four channels-left, center, right, and surround-that were encoded onto the program material's stereo soundtracks.
Dolby Surround Pro Logic II is an improved matrix decoding technology that provides better spatiality and directionality on Dolby Surround program material; provides a convincing three-dimensional soundfield on conventional stereo music recordings; and is ideally suited to bring the surround experience to automotive sound. While conventional surround programming is fully compatible with Dolby Surround Pro Logic II decoders, soundtracks will be able to be encoded specifically to take full advantage of Pro Logic II playback, including separate left and right surround channels. (Such material is also compatible with conventional Pro Logic decoders.) 
Dolby Digital identifies the use of Dolby Digital (AC-3) audio coding for such consumer formats as DVD and DTV. As with film sound, Dolby Digital can provide up to five full-range channels for left, center, and right screen channels, independent left and right surround channels, and a sixth ( ".1") channel for low-frequency effects.
Dolby Headphone is a unique signal processing system that enables conventional stereo headphones to convincingly portray the sound of a multispeaker surround sound system in actual listening rooms. It can be incorporated into virtually any type of audio or video product that features a headphone output, and is also used by airlines to heighten their passengers' inflight entertainment experience.