What Is Dolby Surround Sound?
Dolby has been enhancing sound for several decades, but the true mother of all surround-sound encoding schemes in home theater systems is Dolby Surround Sound (introduced by Dolby Laboratories in 1982). You’ve probably seen advertisements for Dolby at the beginning of movies. But you’ve probably never known exactly what Dolby does.
Here are some details on Dolby Surround Sound:
Dolby Surround Sound encodes four analog audio channels into two channels for storage and transmission or both. If you play Dolby Surround on a normal stereo, you get two channels. If you play it on a Dolby Surround-enabled decoder device, the device separates the full four channels for playback.
With Dolby Surround, the four channels encode front left, front center, front right, and monophonic surround as their channels. The left, center, and right channels are full-range channels, meaning that they carry the full range (20 Hz to 20 kHz) of audio frequencies. The fourth (rear) surround-sound channel is a limited bandwidth channel, meaning it carries only a subset of the frequency range (not the real low-frequency or high-frequency stuff).
At first, consumer audio/video receivers with Dolby Surround decoders could separate only the left, right, and monophonic surround speaker channels. However, with the advent of Dolby Pro Logic in 1987, receivers could decode the center channel as well. The consumer devices just took awhile to develop the same processing power that the more expensive movie theaters had onboard.