Deciphering Surround Sound Essay, Research Paper
DECIPHERING SURROUND SOUND
FOR HOME THEATER
In recent years there have been many advancements in the world of home entertainment, arguably the most popular of these being the inset of theater quality Surround Sound at home. The dramatic growth and popularity of surround sound has spawned more and more companies trying to get their piece of the action. The obvious advantage of this competition is constantly advancing technologies and great variety in products that span every price point and budget. The downside to all of this variety and cutting edge technology is the often confusing learning curve and deciding which system will best suite your home entertainment needs. The following information should help dispel the mystery of surround sound and bring you up to date with the most recent developments. Though there are other brands and formats out there to choose from we are going to focus on the three most popular and successful companies in the surround sound world today, Dolby Labs, Digital Theater Systems, and LucasFilm. We ll start with Dolby Labs and their older, but still in wide use, formats: Dolby Surround and Dolby Pro-Logic.
The Dolby Surround process involves encoding four channels of information–Front Left, Center, Front Right, and Rear Surround into a two-channel signal. A decoding chip then decodes the four channels and sends them to the appropriate destination, the Left, Right, Rear, and Phantom Center. The center channel is derived from the L/R front channels not a center speaker. The result is a more balanced listening environment in which the main sounds derive from the left and right channels, the vocal or dialog emanates from the center phantom channel, and the ambience or effects information comes in from behind the listener. The sensation of sounds moving from front to rear and left to right adds more realism to the viewing/listening experience by placing the viewer in the action. Dolby Surround is easily useful in both musical and film sound recording.
Dolby Surround does have its limitations, however. With the rear channel being basically passive, it lacks precise directionality. Also, overall separation between channels is much less than a typical Stereophonic recording. Dolby Pro-Logic addresses this issue by adding hardware elements in the decoding chip that emphasize important directional cues in a movie soundtrack. In other words, the decoding chip will add emphasis to directional sounds by increasing the output of the directional sounds in their respective channels. This process is very effective for film soundtracks and adds more accuracy to effects such as explosions, planes flying overhead, etc. There is greater separation between channels. In addition, Dolby Pro-Logic extracts a dedicated Center Channel that more accurately centers the dialog which created the need for a fifth speaker dedicated to the center channel. Although Dolby Pro-Logic is an excellent refinement of Dolby Surround, its effects are derived strictly in the reproduction process, and even though the rear surround channel employs two speakers, they are still passing a monophonic signal limiting motion and sound placement cues. This brings us to Dolby Labs current and most popular format called Dolby Digital, also known as AC-3, or 5.1 Surround
Dolby Digital adds both accuracy and flexibility by adding stereo rear surround channels that enable sounds to emanate in more directions, as well as a dedicated Subwoofer Channel to provide more emphasis for low frequency effects. Dolby Digital is often referred to as a 5.1 channel system, which stands for five discrete surround channels plus the one dedicated subwoofer channel. Unlike Dolby Pro-logic, which requires a rear channel of only minimal power and limited frequency response, Dolby Digital encoding/decoding requires the same power output and frequency range as the main channels. Dolby Digital encoding on DVDs, laserdiscs, and satellite programming is very common and has solidified this format in the
Dolby Labs, however, is not the only player in the home surround sound market. Digital Theater Systems has also adapted its surround sound process for home use. It is a 5.1 system just like Dolby Digital, but since DTS uses less compression in the encoding process, many feel that DTS has a better result on the listening end. In addition, while Dolby Digital is mainly intended for the movie soundtrack experience, DTS is also being used in the mixing and reproduction of musical performances. Although DTS is a 5.1 system, a DTS-equipped amplifier or receiver is required to accurately decode the signals imprinted on DTS-encoded media.
Finally we have THX (Tomlinson Holman Experiment) owned by LucasFilm ltd. Many consumers are under the impression that THX is an altogether different surround sound system when in actuality it is just a certification program that manufacturers use to see if they meet the standards that LucasFilm has set for optimal surround sound performance. The idea is that sound tracks under THX are reproduced exactly as the filmmaker intended. Components, from receivers and amps to speakers, have to meet certain performance and construction requirements in order to get the THX logo on their products. In order to achieve the full effect of this certification process, all the components in your system must bear the THX logo.
The Next Generation
Although all the surround sound formats in use today, Dolby Pro-Logic, Dolby Digital, DTS and THX, result in a much more realistic listening experience for watching films, they all have their limitations. With that in mind, LucasFilm-THX and Dolby Labs have teamed up to develop the most realistic Home Theater Surround Sound process developed so far. Originally developed for the theatrical release of Star Wars: Episode I and applied to other current film releases, this process has been adapted for use in Home Theater applications.
Rather than working from “ground zero” to develop a totally new format. THX Surround EX (its official name) is actually based on the technology already developed for Dolby Digital 5.1. The new process adds a third surround channel that is placed directly behind the listener. Incase you re losing count, that makes a 7.1 system: Left Front, Center, Right Front, Surround Left, Surround Right, Subwoofer, with Surround Back Left and Surround Back Right actually being a single channel. Does this mean that someday the back surrounds will be split into two independent channels, too? Who knows?
Although THX Surround EX is not very compatible with DTS Decoding, it is very much compatible with Dolby Digital 5.1. Since the Surround EX signals are matrixed within the Dolby Digital 5.1 signal, software titles encoded with EX can still be played on existing DVD players with Dolby Digital outputs and decoded in 5.1 on existing Dolby Digital Receivers. Although you may end up buying new EX-encoded versions of films you already have in your collection, when you finally get your EX setup running you will still be able to play your current DVD’s through a Surround EX Receiver.
THX and Dolby Labs aren’t the only ones in the enhanced-surround sound business. DTS has come up with its own 6.1 channel system DTS-ES and DTS-ES 6.1 Discrete. As with THX Surround EX, the new DTS-ES and DTS-ES 6.1 Discrete formats are backwards compatible with current DTS Receivers and DTS encoded DVDs. THX claims, however, that non-EX 6.1 schemes will not decode EX-encoded material correctly.
As you can see there are seemingly endless possibilities in the world of Home Theater. Like the enhanced systems above, future formats promise to be forward and backward compatible as technology moves forward, and with a basic knowledge of what each system has to offer and a peek at what s to come you will be able to choose a system that will give you years of entertainment.
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