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Sound Technology

Some of the most important advances in home theater have come in sound technology. Improvements in home theater sound have brought the "feel" of cinema sound to the comforts of one's own home.

Surround Sound

The first big step to the reality of home theater was the evolution of surround sound. Dolby Surround® for the home was introduced in 1982. Dolby Surround decodes the surround channel so it's played back like it was recorded in the movie sound studio.

Surround sound started in cinemas for dramatic effect and eventually evolved to create realism to the theater experience through sound panning and added sound depth.

Even though surround sound made a big step technologically, it still had a way to go to recreate the full sound intended by film makers.

Dolby Pro Logic®

The next step in home theater sound technology was the advancement of surround sound with Dolby Pro Logic. Debuting in late 1987, Dolby Pro Logic stepped forward with the capability to decode an active center channel to its own speaker.

The use of an active center channel brings out a clearer dialogue and allows the right and left front speakers to be spaced farther from the center for a wider, richer distribution of sound.

Dolby Pro Logic decodes and converts two channel stereo audio from a VCR, Laserdisc Player, or television broadcast into four channels of audio.

One channel goes to the left speaker, one to the center, and one to the right. The fourth channel goes to the surround speakers which add aural "presence," a quality needed for true Home Theater.

Initially, this leap in quality was limited to expensive, high-end systems. But now Dolby Pro Logic is an affordable way to achieve high performance home theater sound.

Dolby Digital differs from Dolby Pro Logic with a better separation of channels and the addition of individual channels for both surround speakers. This allows for more precise sound fields and adds more depth and realism to the home theater experience.

Dolby Digital does not eliminate the need for a Dolby Pro Logic decoder. Because of the amount of material that exists as the traditional two channel stereo sound, Dolby Prologic is still needed to break those two channels into four for a fuller surround sound.

All Dolby Digital decoders will have a Pro Logic decoder built-in for that purpose. And the good news is that as the Dolby Digital receivers are becoming more popular, they are also becoming more affordable for many people.

Dolby Digital has been adopted as the audio standard for Digital Versatile Discs (DVDs) and High Definition Television (HDTV) which are the latest home theater advances heading soon to the general market.

At this time Dolby Digital is available in over 6,000 cinematic theaters and very high-end home theater systems. Many laserdiscs are already released with 6-channel digital technology while many more are currently being produced.


THX is not a brand name for home theater equipment, but is a licensing technology to ensure the highest standards for the best reproduction of theater-type sound. Dolby and THX are not in competition with one another, and they often work together to create high quality theater and home theater experience.

THX is the gold star standard for acoustics, and speaker placement, and certifies equipment that is capable of playing the best sound.

The development of THX audio was the result of director George Lucas' efforts to achieve truer sound reproduction in movie theaters. His Lucasfilm company patented the standard which was later translated to the home format.

Home THX changes the sound created for a large theater to sound more suited for the smaller and closer environment of home theater. To achieve this, a home THX system must include certified Home THX equipment.

As a result, THX has become the premier licensing standard for controllers, power amplifiers, loudspeakers, acoustically transparent front projection screens, and audio interconnects.

A Home THX Audio System carries a higher price tag, but has many advantages over the standard surround systems including:
Clearer Dialogue

Better Localization of On-Screen Sound (so sound pans realistically with movements)

Effortless bass reproduction(for rumbles, explosions, and other impact sounds)

Enveloping Surround Sound (for all-around sound fields)

Wide Frequency and Dynamic Ranges (able to reproduce the full range of sounds recorded at the mixing studio)
Dolby Digital® / AC-3®

The newest surround sound technology from Dolby is Dolby Digital®, also known as Dolby AC-3®. Introduced in 1992 with Batman Returns, Dolby Digital was designed to maximize theater sound by taking advantage of the way we hear.

It 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 available options in decoding. Program material recorded in Dolby Digital can be played as mono, stereo, Dolby Surround or Pro Logic, or to the full 6 channel capacity.