A surround-sound system usually consists of five channels of sound plus a low-frequency channel for a subwoofer. (If a DVD has been encoded for full, discrete five-channel surround sound, it will say on the box "5.1 Dolby Digital.") The five channels consist of front-left, front-right, front-center, rear-left, and rear-right. The rear channels are great fun for chase scenes and explosions, but, when a disc is well-engineered, they also contain the subtle sounds of ambience, giving you the sense of immersion in a scene. The center channel on a surround-soundtrack contains most of the dialogue. This is the main reason for investing in a surround-sound system. When dialogue has its own speaker, it is much clearer. A DVD player's "audio set-up" menu gives you a choice between two channels (in which case the center and rear channels get split between your left and right speakers) or five channels, but not three. To get that center channel, you need all five.