CNET's quick guide to surround formats

From Edison's first wax-cylinder machine to the mid-1950s, home audio was always mono. Stereo took off in the '60s, and the first surround format to take hold and flourish was Dolby Surround in 1982. Dolby Surround is a matrix format; that is, its surround effects are encoded in two stereo channels. Many of today's surround formats are discrete and feature six separate tracks.

Some DVDs feature multiple surround formats--for example, Dolby Surround, Dolby Digital, and DTS--on a single disc. This brings up another angle to the surround story; to enjoy the full sound potential of, say, a DTS-ES-encoded DVD, you need a receiver that processes DTS-ES. In other words, formats exist in both software and hardware. Other formats, such as Dolby Pro Logic II and DTS Neo:6, are found only on hardware--receivers, HTIBs, DVD players, and so on--and are applied to processing software or music sources, such as CDs, DVDs, MP3 files, and radio.

When we designate the maximum number of speakers/channels for each format, such as 5.1 or 6.1, we're referring to the number of front, center, rear, and possibly center-rear speakers (the .1 refers to the subwoofer) that the format can use. Stereo, a.k.a. 2.0, is a two-channel format. Check out the diagram below to see how they are set up in a room. Note that even though 7.1 systems use two back-surround speakers, the same channel of information goes to both of them.