The first big breakthrough in home theater was the evolution of surround sound, which was first introduced in 1982 by Dolby Surround®. Dolby Surround works by decoding the surround channel so that it's played back like it was recorded in the movie sound studio.
Dolby Pro Logic®
The next step in home theater sound technology came in 1987 with the advancement of surround sound with Dolby Pro Logic, which is able to decode an active center channel to its own speaker. This allowed for clearer dialogue and for the left and right front speakers to be spaced farther apart to give a richer distribution of sound.
In simple terms this technology decodes and converts two channel stereo audio from your VCR, DVD or TV into four channels of audio (by going to your surround speakers) - giving your current system the quality it needs for a true home theater experience.
Dolby Digital®
The newest surround sound technology from Dolby is Dolby Digital®, which provides six discrete channels of full range sound: front center, front left, front right, rear left, rear right, and the bass or subwoofer. Dolby Digital technology also allows for more decoding options, so that program material recorded in Dolby Digital can be played as mono, stereo, Dolby Surround or Pro Logic, or to the full 6 channel capacity.
While Dolby Digital offers a better separation of channels and the addition of individual channels for both surround speakers than its predecessor Dolby Pro Logic, you still need a Dolby Pro Logic decoder because of the amount of material that still uses the traditional two channel stereo sound (and only a Dolby Prologic can break those two channels into four for a fuller surround sound). Luckily you won't need two separate decoders because Dolby Digital has a Pro Logic decoder built right in. If you're planning on buying a Digital Versatile Discs (DVD) or High Definition Television (HDTV) than you'll want to go Dolby Digital - it's as close as you'll get to the sound and feel of movie theater without having to leave your sofa.
While THX sounds like it is a brand name, it is actually a licensing technology for home theater equipment, which is used to ensure the highest standards for the best reproduction of theater-type sound. Dolby and THX often work together to create a high quality home theater experience. In short, THX has become the five star standard for acoustics and speaker placement and certifies the equipment that is most capable of playing the best sound.
Thanks to a THX patent, sound which was originally created for the movie screen is now suited for a smaller and closer environment - your home theater. Be sure that your home equipment is certified THX otherwise you're not getting the real thing.
While it comes with a high price tag, the advantages of a THX audio system over standard surround systems are clearer dialogue, easy bass reproduction (great for action movies with lots of explosions), enveloping surround sound and wide frequency and ranges.
