Your Old TV - Two Channel Stereo Sound
Old fashioned NTSC television gives the listener two channels of audio - right and left - which is commonly known as "stereo" and is similar in quality to a FM radio broadcast.
Digital Television - 5.1 Channel Dolby Digital Surround Sound
The same sound that is used in many digital movie theaters and nearly all DVDs, Dolby Digital surrounds you with 5.1 channels of CD-quality surround sound: a center channel, left and right front channels, and left and right rear channels. The ".1" channel is set aside for the optional "sixth" channel, the subwoofer. The subwoofer produces the powerful low frequency sounds that you can "feel", such as deep bass in music or the thunderous rush of a fighter jet streaking across the screen.
The diagram below shows the position of each of Dolby Digital's 6 channels in a typical room.