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Buying
Guide: Home Theater in the Digital Age
by
Outpost.com
Sound is as integral to the home theater experience as the picture. Think about what makes you get all choked up watching The Way We Were: it's not just the poignant dialogue, but it's also the gut-wrenching soundtrack jerking every tear from your eye (all right Barbara, you go girl).
I've heard that Godzilla delivers some profound dialogue himself (as of this article the movie hadn't yet been released), but it's probably the earth-shaking foot stomps that'll secure his Oscar nomination. And it's the sound of said foot stomps - hurling toward your chest at 96 dB - that really makes the movie intense.
The point is, that although many movie-lovers become preoccupied with owning a big-screen television, the screen size is no more vital to the quality of the entertainment gestalt, then the sound.
A brief history of surround sound
Traditional two-channel stereo sound was introduced in the 1950s to make recorded music seem more like a live performance. Stereo works by essentially "tricking" your ears into perceiving the sound as coming from a place located behind the speakers instead of coming from the speakers themselves. This is done by utilizing a time delay between the left and the right speakers during the mixing process. This time delay causes the human ear to perceive a depth to the sound even though sound is coming from the two-dimensional environment of a pair of speakers.
People so enjoyed this new-found spaciousness of sound, that stereo manufacturers came out with Quadraphonic Sound around 1972. Quad involved four speakers instead of merely two, but was an unmitigated failure probably because the cost and clunkiness of the equipment far outweighed the sonic benefits.
Also in the 1970s, action and disaster movies became increasingly popular and movie studios began to realize the thrilling potential of premium sound in the theaters. One of the most memorable films that did a lot to increase public interest in a movie's sound was Earthquake in Sensurround. Even though Sensurround didn't really resemble the Dolby Surround Sound of today, it allowed viewing audiences to experience the power of a movie's soundtrack. Sensurround didn't utilize spatial techniques, but instead cranked up the bass big time, so you felt the city crumble right in your chest.
In 1986, Dolby Labs introduced a home version of its surround sound called (simply enough) Dolby Surround Sound which was licensed by all of the major stereo manufacturers. It involved a four channel configuration instead of a five-channel one because it was unclear at that point how a center-channel speaker would work within the confines of a home system. The center channel dialogue information was split up, with half being sent to the left main and the other half being sent to the right main speaker. This configuration worked OK, except that the dialogue was often-times obscured by the other sounds coming from the two main speakers like the film's sound effects and music soundtrack.
Dolby Pro Logic
In 1989, Dolby released a 5-channel home version of its software called Dolby Pro Logic surround sound which employed a center-channel dialogue speaker just like its professional movie theater older brother. The dialogue speaker is merely placed on the top or underneath the TV set and it gives the illusion that the actors' lines are coming right from the TV screen.
VHS videocassettes, as well as laserdiscs, and DVDs are encoded with the Dolby signal. When they're played back through a receiver sporting a Dolby Pro Logic chip, different sounds are sent to different speakers yielding true surround sound. Dolby Pro Logic code is also transmitted though the airwaves so you can get surround sound on movies and TV shows broadcasted through the airwaves and through DSS. The only issue is cable - some systems broadcast in stereo and in surround sound. But to this day, the majority of cable system don't even deliver shows in stereo, let alone in surround sound. Check with your cable company and see what's up in your town.
Yamaha's Digital Soundfield Processing
Around the same time, audio manufacturers like Yamaha were developing ways to enhance Dolby Pro Logic and give it additional depth. One purpose was to make your living room have the same depth and large-scale acoustical properties as a major movie theater. Yamaha created a system called Digital Soundfield Processing which combined the steering logic of Pro Logic surround sound with digital signal processing to create variations on surround sound for home movies, videos, and laserdiscs, as well as for music.
The classic Yamaha DSP system utilizes a seven-speaker configuration featuring two main channels, two front effects channels, two rear channels, and a center channel. Even Yamaha's 5-channel receivers with DSP incorporate seven channels of information for great sound even at the low prices. But DSP isn't just for movies, but for music as well. Yamaha engineers took acoustical blueprints of famous concert venues from stadiums, to symphony halls, to jazz clubs. These blueprints then became models for the DSP software and allows the user to transport a CD's studio performance to a live venue for a more dynamic, live sound.
THX
Besides Yamaha, other companies worked hard to improve upon Dolby Pro Logic. One was film director George Lucas' company THX. THX was started by Lucas and his chief engineer Tomlinson Holman because Lucas understood the impact that sound and sound effects had on viewing audiences. Sound after its introduction, THX became the quintessential surround sound system during the mid-1990s. Contrary to popular belief, THX is not its own format, but rather a set of rigid standards based around the Dolby Pro Logic system. Speakers, amplifiers, and receivers are THX-certified only if they adhere to these standards - an amp must meet certain power output specifications, the same for a speaker's efficiency and frequency response, as well as the performance of the receiver's Pro Logic chip itself.
Because the standards are so rigorous, THX systems are still very expensive. And while they are still the darlings of custom installers who sell $20,000 custom-built in-home screening rooms, THX surround sound is being given a run for its money from newer digital technology.
Dolby Digital
In 1996, Dolby labs introduced their latest version of home surround sound - Dolby Digital. It was first called AC-3 which was actually the name of the coding scheme that they used to encode the digital data. AC-3 was initially relegated to laserdisc, because it requires a digital source and at the time of Dolby Digital's introduction, laserdisc was the only movie source with such an output. (FYI: a laserdisc has a digital audio output, but an analog video output, Digital Satellite, and DVD are currently the only video sources that are completely digital, until HDTV comes out later this year).Now AC-3 is referred to as Dolby Digital, and is featured in all DVD players, as well as new models of laserdisc players. Rumor has it that it will also be available through DSS broadcasts sometime in the future. Dolby Digital is an encode/decode process so that means that the Dolby Digital code has to first be encrypted onto the disc and then has to be played back utilizing a DVD or laserdisc player that is either Dolby Digital or Dolby Digital-ready, and a receiver of the same feature set.
Beware of the distinction between true Dolby Digital and Dolby Digital-Ready. True Dolby Digital means that the actual Dolby Digital microprocessor is inside the unit. Dolby Digital-Ready means that the unit doesn't actually contain the microprocessor itself, but rather has a six-channel audio input to interface with a unit that does. A DVD player can either have a built-in Dolby Digital microprocessor, or just have the correct coaxial digital output to hook up directly into a receiver with the Dolby Digital processor. Conversely, a surround sound receiver can either have the Dolby Digital chip, or merely accept a six-channel input from a DVD player with a built-in chip. The bottom line is that you must have at least one component that has a built-in chip and one that is Dolby Digital-Ready.
Dolby Digital uses digital processing so it is much cleaner than standard analog Pro Logic. It delivers broader frequency response and a more impressive signal-to-noise ratio. But besides better specs, Digital Dolby also utilizes a "5.1-channel" format which delivers two more important benefits over analog Pro Logic: stereo rear channels and a discrete subwoofer output.
Even though standard Dolby Pro Logic has five speakers, it is only a four-channel system. The front channels are stereo, and the center channel has its own output information. But the rear channels are monaural - the same exact information comes out of both the left rear and the right rear speaker. Dolby Pro Logic delivers ample sound effects as long as they are from front to rear (or rear to front). But there is no real side-to-side motion. On the other hand, Dolby Digital sports true stereo rear speakers, so sound can travel front-to-rear and side-to-side.
Dolby Digital also delivers excellent bass response. That's because it has a separate output which only consists of low bass information designed specifically for use by a subwoofer. A subwoofer is a speaker designed specifically to produce low bass sounds. It looks like a very short end table and contains both a large woofer (ranging in size from 8-inches to 15-inches), and a dedicated power amplifier. A subwoofer has its own built-in power amp because the low bass output is generally a line-level unpowered output that needs amplification. It takes a massive amount of power to produce clean low bass sound, so powered subwoofers usually have built-in amps rated at 100 watts or greater. Also, low bass is inherently a monaural phenomenon, much due to the fact that the human ear cannot discern stereo separation in frequencies below 100 Hz. That's why the dedicated subwoofer channel in Dolby Digital is mono not stereo.
This dedicated low bass channel in the Dolby Digital format is referred to as the ".1" channel in the 5.1 configuration. That's because it is not a full-frequency channel. The fact that the low bass frequencies have been removed from the rest of the 5-channel section of the soundtrack makes for clearer effects, cleaner dialogue, and, of course, better bass. It also means that you really need to get yourself a subwoofer in order to get he full benefit of the system. Conventional wisdom dictates that a home theater system is about a zillion times better with a subwoofer than without one (that's a technical fact, by the way).
Digital Theater Systems
Of course, there can't just be one type of surround sound in this world of mega-choices. So Dolby's "Burger King," is a new company called Digital Theater Systems or DTS. DTS has been a competitor of Dolby at the professional movie theater level for a few years and has just started to license their surround sound technology to consumer electronics manufacturers for home use. Right now DTS surround sound processing is found mostly in high-end receivers above $700, but that will change and the prices will come down dramatically by next year. Like Dolby Digital, DTS is an encode/decode process so all source material must be encoded with DTS and then played back utilizing a receiver with a built-in DTS processor. You cannot play a CD or DVD encoded with DTS in a non-DTS receiver, it sounds like noise.
Unlike Dolby Digital's commitment pretty much exclusively to movies, DTS launched its technology with CDs and laserdiscs. Unlike Dolby Digital you can just have a digital output to hook into a digital receiver. It re-released many famous discs (e.g. Allman Bros. Live at Fillmore East, and Alan Parson's Project I Robot) with DTS surround sound. According to many critics, DTS' processing is much more conducive to music than Dolby Digital, and these classic rock discs sound awesome with DTS. DTS boasts a higher data rate than Dolby Digital which increases in the amount of digital information used, which translates into a more audiophile-type of CD than the original sans-DTS versions. Also, DTS is only compressed 3:1 vs. 12:1, which also translates into purer sound output.
DTS is also in the process of releasing movies on DVD utilizing its surround sound, and these titles should be out as soon as this Fall. But beware, first generation DVD players will not play DTS DVDs - you need the newest generation players.
When we asked industry experts which format they predict will prevail, they weren't taking sides yet. Here's what Tom Graham national marketing director for Yamaha Electronics Corporation, USA had to say: "We at Yamaha realize that both DTS and Dolby Digital have roughly the same number of movie theater screens worldwide, so we've made the decision to support both formats - they both have value for the consumer. Our job at Yamaha is to produce products that people want to have. If they go to a theater and see a movie in either DTS or Dolby Digital, then they might want either format so our DSP-A1 has both."
Which format will be left standing - Dolby Digital or DTS - is anybody's guess at this point. Dolby has had the monopoly on surround sound processing from the beginning and they sure are the safe bet. But if DTS has its way, all receivers will include both types of processing. Right now, most of the major surround sound receiver manufacturers are looking into both. Whichever you decide, it will certainly be a huge step up from the baby speakers built into your TV set.
By Noah Herschman
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