Surround Sound Made
Easy
Confused by surround sound? Don't sweat it -- if you want
to know the truth, most people are confused enough by just ordinary stereo. After all,
more people probably have one speaker sitting on the floor in a corner and the other
sitting on a shelf behind a ficas bush than have them sitting spaced equally from the
listening position. At least you know where you're at when the speakers are called left
front, center, right front, and rear. But surround isn't really hard to understand once
you get past the alphabet soup of surround format acronyms.
It all goes back to Star Wars, which was the first Dolby
Stereo film. Stereo is a misnomer, since the film actually had multiple channels of
sound (the process was later renamed Dolby Surround -- at least the version intended for
home consumers was). Audiences thrilled for the first time to the sounds of flyovers that
went from the screen to the rear of the theater -- and the sound of energy weapons
discharging all over the place, not to mention the powerful, all-inclusive sound of the
Deathstar going nova! This was the birth of sound effects that were as thrilling as the
action on the screen.
Multichannel surround in theaters calls for a large number
of speakers lining the sides and rear of the theater. Up front, behind the screen, there
are left- and right-channel speakers, plus a center-channel speaker, which reproduces all
of the onscreen dialog. In addition, most theaters have a subwoofer, which reproduces the
incredibly low sounds that have become integral to so many big-budget pictures.
Most home theaters feature left, center, and right speakers
at the front, as well as a subwoofer. But they only have one left and one right surround
speaker as opposed to the big array found in theaters.
Recently -- once again starting with a Star Wars
film, this time Episode One: The Phantom Menace -- Dolby has introduced a new
surround scheme for theaters, Dolby EX, which adds a rear center channel (played
through several speakers), in addition to the left and right surround channels.
At home, though, surround stayed a bit simpler. No, don't
laugh -- it is, really.
Okay, there is one complication -- there's more than one
type of surround sound. However, all of them do essentially the same thing and here's the
cool part: Most surround-sound processors and receivers automatically choose the correct
type of processing, so you don't really need to worry much about it. But since I'm sure
you're the enquiring type, here's a cheat sheet on the differences between them.
If you watch movies on VHS tapes, you'll be using Dolby
Pro Logic, which is not a discrete surround format. Technically, it's a matrixed
system, which encodes center-channel and rear-channel information into the signal carrying
the right and left channels. Pro Logic extracts the information from the two encoded
channels and steers it to the appropriate speakers -- left and right soundtrack spatial
information to the right and left front speakers, dialog to the center-channel speaker,
and effects to the rear. Dolby Pro Logic sends the same signal to both rear speakers and
adds reverb to simulate spaciousness. And it’s not only VHS tapes that include a
Dolby Pro Logic soundtrack, so do many TV shows. Any receiver marketed as suitable for
A/V, even the least expensive, includes Dolby Pro Logic processing.
 Digital 5.1 Surround
is, as the name suggests, digital, so it needs a digital format to work with. It was
developed for laserdiscs and continues to be used with DVDs. It employs five
full-frequency, discrete audio channels (front left, center, front right, right surround,
and left surround) plus a separate channel (that's the .1), which routes the bass
information to a separate subwoofer. Digital 5.1 surround sends different information to
each of the rear surround speakers, as opposed to Pro Logic’s summed information.
Two competing formats provide this 5.1-channel surround for
the home: Dolby Digital (formerly known as AC-3) and DTS
(Digital Theater System). DTS offers some theoretical advantages over Dolby Digital
(higher bit rate; less data compression), but Dolby Digital is more deeply established in
the marketplace -- almost all DVDs have Dolby Digital soundtracks, only a handful, in
comparison, have only DTS, and an increasing number have both.
Older A/V receivers -- as well as some inexpensive models
-- will only process Dolby Pro Logic internally, but advertise themselves as Dolby
Digital ready or 5.1 ready. That means the receiver lacks its own Dolby Digital
decoder, but has the six inputs needed to accept the processed 5.1-channel information
from a DVD player with built-in Dolby Digital processing or from an external Dolby Digital
processor. Dolby Digital is standard on most mid-priced A/V receivers and DTS processing
is included on some as a value-added feature. At the higher end of the spectrum, almost
all receivers have both -- and some have newer, not yet universal, surround capabilities
as well. If a receiver decodes several different types of surround encoding, it will
probably automatically detect the most appropriate option and set the processing for
playback.
Many receivers also feature an assortment of DSP
(Digital Signal Processing) modes that have labels such as CHURCH, STADIUM, SMALL CLUB,
and so on. Supposedly, these allow you to create surround sound out of a stereo signal,
but they generally sound like crap. Unfortunately, some listeners are convinced they should
like these effects and use them all the time. Use your own ears, of course, and decide
whether or not to use them according to your own taste, not some critic's snarky opinion.
Recently, several companies have introduced processors with
extra surround channels -- one proposed standard would utilize a 7.1 surround scheme,
another went so far as to suggest 9.1! And, as previously mentioned, there's Dolby EX,
which is 6.1. It remains to be seen if consumers are ready to keep adding extra speakers
and channels. I am dubious as to whether any of these stands a chance of popular
acceptance. (Please note: This has nothing to do with whether or not they sound better.)
The other bit of alphabetic gobbledygook you need to know
is THX. THX is a certification system designed to assure consumers that they
are hearing what the movie's director intended. THX started as a certification program to
ensure that movie theaters delivered good sound and now there's a similar program for
home-theater setups: A/V equipment can be THX certified, as can installation specialists
and even the software (DVDs) you buy.
THX certification for A/V equipment lets you know that the
equipment can deliver at least a certain amount of undistorted sound and meet
certain other specifications. However, not every manufacturer applies for THX
certification -- some don't agree with THX's specifications, while others simply don't
feel the need for anyone else's approval. So you can't assume that a product that doesn't
have a THX-certified sticker on it didn't meet THX spec.
There's also THX certification for software, however -- and
there nobody's arguing. If you see a DVD with the THX logo, you can be assured that you're
getting good sound.
So let's review. Surround started as a way to add extra
excitement to films. Audiences loved it and wanted to take it home with them. There are
several different types of surround, but most high-quality contemporary home-theater
products are capable of sorting out the details without your having to obsess over them.
Surround sound is easy.
What do you need to enjoy modern surround sound?
A typical system consists of: an A/V receiver; five
loudspeakers and a subwoofer; a high-quality source, such as DVD; and a large-screen TV,
rear-projection TV (RPTV), Digital Light Projector (DLP) and screen, or widescreen plasma
TV.
A more complex home-theater setup would split the functions
of the receiver into its component parts: usually a surround-sound processor and power
amplifiers. Since you need five channels of amplification, you could get five separate
amplifiers -- and some hard-core home-theater buffs do --- but there are also
single units containing five channels of amplification and a whole world of two- and
three-channel amps that can be combined as needed.
The good news is that the basic, do-everything audio
receiver has come a long way. The sheer amount of technology available to the consumer at
an affordable price these days is staggering.
...Wes Phillips
wes@onhometheater.com
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