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How Surround Sound Works

Surround Sound is the term commonly used to describe a system in which the sound output appears to surround the listener — that is, the technology gives the impression that sounds are coming from all possible directions. Surround sound is a way to provide a more realistic and engaging experience. Sitting in front of your standard television or playing a computer game with basic $10 stereo speakers plugged in will provide you with sound. You hear the music, voices and other sounds coming to you from straight ahead. Using a surround sound system, however, you'll hear variances in the sound and and it will be presented to you from different directions. For example, the car driving off screen sounds like it is coming from the left. While playing a 3D shooter game, the rocket gun blasts sound as if they are being shot from overhead or grenades sound like they are exploding at ground level.

Today consumers demand immersive entertainment and surround sound plays a big part in delivering engaging media. To this end, there's no lack of options when it comes to surround sound technology and systems.

All technical aspects aside, Surround sound works because multiple audio channels are received through speakers that are positioned at various locations in the room. This is programmed into the source and the sound tracks are decoded when the source is played. While this may seem simplistic, it's important to remember sound systems started out with monophonic sound, a single channel system. In monophonic (mono) sound systems, the signal sent to the sound system is encoded as one single stream of sound — and the sound is usually received through a single speaker.

Key Terms to Understanding Surround Sound: 

Surround Sound
Surround sound is a term used to describe a type of audio output in which the sound appears to "surround the listener" by 360 degrees.

Dolby Digital
A standard for high-quality digital audio that is used for the sound portion of video stored in digital format.

Channel
An individual discrete audio track. When referring to more than two channels it is called multichannel.

 

Advancements led to stereophonic sound (stereo) where the sound was split between two channels, left and right. Stereo sound enabled listeners to hear some ambiance of the production — for example, a recording of a live concert in stereo where you begin to hear playback from extraneous noises at the performance. Surround sound takes it a step further by producing a live-quality effect. If you're at an actual concert, you hear sound from behind you, and listening to a recording in surround can produce the effect of this noise — coming from behind you, or to the right, or even from above you and moving down. Surround sound adds realism and a new field of depth to your listening experience. This is accomplished not only because you have more speakers for output, but because the sound recording itself contains more audio channels.

The A/V (audio/video) Receiver
At the heart of every home theater is an audio/video receiver (A/V). Using a DVD movie as an example, the audio is encoded when the DVD is produced by packing multiple audio channels into a compressed format for storage.  When you play the DVD movie, your DVD player or A/V receiver (commonly called a
a home theatre receiver) decodes the encoding scheme (i.e. Dolby Pro Logic II for example). Decoding capabilities of an A/V receiver are built in. Most A/V receivers today can decode Dolby Digital and Digital Theater Sound (DTS), while higher-end receivers may also include DTS-ES or THX Surround. Today's A/V receivers allow you to control the video source and other video options, but for sound you'll need it to route the sound from different sources (TV, DVD, VHS), control bass, treble, and volume. You can amplify signals to the speakers, and modern A/V receivers also handle the all-important surround sound decoding.

5.1, 6.1 and 7.1 Channel Surround Sound Systems
Both Dolby Digital and DTS are 5.1 channel formats.  5.1 Surround Sound is a multichannel sound technology that produces five channels of sound in the left, right, center, left-surround and right-surround positions. These five channels are the minimum required to produce 5.1 surround sound. The .1 represents the channel for LFE (low frequency effects), which is usually sent to a subwoofer. 

While 5.1 Surround Sound has been the standard for some time now, newer A/V receivers are capable of delivering 6.1 Surround Sound. 6.1 multichannel sound technology uses the same set-up as a 5.1 system, but it has the addition of a sixth speaker that takes the rear-center surround position (or back surround position) to provide a more 3-D sound. 6.1 Surround Sound uses Extended Surround sound formats (THX Surround EX, DTS-ES).

Moving forward, we now also have 7.1 Surround Sound, which splits the single rear-center surround speaker into individual left- and right-rear surround. These systems are not a true discrete 7.1 channel system as 7.1 formats don't currently exist. In a true discrete 6.1 surround system, the back center surround position is separate from the surround left and surround right positions. A 7.1 channel system uses matrixed extended surround where the left-back and right-back (rear-center surround) multichannels are blended together and stored.

     

Click each image to view a larger diagram of speaker set-up for 5.1, 6.1, and 7.1 channel surround sound. Images are not to scale.

Common Surround Sound Formats

Dolby Surround: Dolby Surround is the consumer version of the original Dolby multichannel analog film sound format — Dolby analog and Dolby SR (Spectral Recording). When a Dolby Surround soundtrack is produced, four channels of audio information (left, center, right and mono) surround are matrix-encoded onto two audio tracks. These two tracks are then carried on stereo program sources such as videotapes and TV broadcasts into the home where they can be decoded by Dolby Pro Logic to recreate the original four-channel surround sound experience.

Dolby Digital: A standard for high-quality digital audio that is used for the sound portion of video stored in digital format, especially videos stored on DVD-ROMs. Dolby Digital delivers six channels in the so-called "5:1" configuration: left, right, and center screen channels, separate left and right sounds, and a subwoofer channel. This is sometimes called surround sound or 3D sound.

Dolby Digital EX: Dolby Digital EX takes the Dolby Digital 5.1-channel setup one step further with an additional center-surround channel (reproduced through one or two speakers) for extra dimensional detail and an enveloping surround-sound effect. Feature films originally released in Dolby Digital Surround EX (the cinema version) carry the encoded extra surround channel in their subsequent DVD releases, as well as onto 5.1-channel digital satellite and TV broadcasts.

Dolby Pro Logic IIx: Dolby Pro Logic IIx is an extension of Dolby Pro Logic II technology. This sophisticated algorithm processes native stereo- and 5.1-channel material to produce 6.1 or 7.1 output channels. Dolby Pro Logic IIx expands choice in playback system configuration (allowing 5.1 , 6.1, or 7.1 playback channels) and, when incorporated into an audio/video (AV) receiver or processor it allows a convenient upgrade path from a traditional 5.1-channel sound system to 7.1 output channels.

Dolby TrueHD: Dolby TrueHD is the next-generation lossless technology developed for high-definition disc-based media. Features of Dolby TrueHD include the following: 100 percent lossless coding technology, up to 18 Mbps bit rate, support for up to eight full-range channels of 24-bit/96 kHz audio, and it is supported by High-Definition Media Interface (HDMI).

DTS: Short for Digital Theater Sound, it is a multichannel surround sound format used in both commercial and consumer applications. DTS was created by the company for which the technology was named, Digital Theater Systems (which is now called DTS as well). DTS is a competing technology with Dolby Digital.

DTS-ES: Short for Digital Theater Sound - Extended Surround. The 6.1 matrixed system enables cinemas to deliver extreme spatial effects that literally surround the audience. A rack mounting DTS-ES decoder creates a back-surround (BS) channel from encoded surround tracks, in typical theatre applications feeding a back-surround speaker array (configured as left-back-wall and right-back-wall for stereo operation). The system is compatible with all current extended surround formats and an auxiliary surround channel is also provided for other applications. ES modes can be selected via automation inputs or via the built-in DTS timecode reader, which detects ES serial numbers for automatic DTS-ES playback.

TruSurround XT: TruSurround XT is the second generation of SRS TruSurround. Building upon its patented predecessor, TruSurround XT solves the problem of playing 5.1 or 6.1 multichannel content over two speakers (or headphones). TruSurround XT accepts input from up to a seven-channel (6.1) audio source and processing a two-channel output. When receiving multichannel content, TruSurround XT virtualizes the channels, creating "phantom" speakers that appear to extend all around the listener. When receiving mono or stereo content, TruSurround XT presents an expansive three dimensional sound field.

 

Did You Know...
Despite the fact that IMAX cinemas use more than 300 speakers, movies (at present time) have only a six-channel digital sound track.

More Surround Sound Terms: Multimedia > Home Entertainment >Surround Sound


Vangie 'Aurora' Beal
Writer, www.Webopedia.com
Last updated: November 18, 2005


Related Links

Dolby Laboratories
Dolby Laboratories develops and delivers products and technologies that make the entertainment experience more realistic and immersive. For four decades Dolby has been at the forefront of defining high-quality audio and surround sound in cinema, broadcast, home audio systems, cars, DVDs, headphones, games, televisions, and personal computers.

DTS Online
DTS, Inc. is a digital technology company  dedicated to delivering the ultimate entertainment experience.  DTS decoders are in virtually every major brand of 5.1-channel  surround processors, and there are more than 300 million  DTS-licensed consumer electronics products available worldwide.

How to Buy Surround Sound
Sound & Vision Online provides the simple steps that will take you from just thinking about a great home theater to actually having one.

Home Cinema Choice Online
The online version of Home Cinema Choice magazine.

Surround-Sound Speaker Placement
This SoundStage article discusses issues and common problems associated with surround sound speaker positioning.

Surround Sound Past, Present, and Future (PDF)
A history of multichannel audio from mag stripe to Dolby Digital. The first commercially successful multichannel sound formats were developed in the early 1950s for the cinema. At the time, stereophonic sound, a concept new to the public, was heavily promoted along with new wide-screen formats by a film industry feeling threatened by the rapid growth of television.

5.1 Channel Setup
This was the first true surround sound setup. There was a four point surround system but the lack of centre speaker prevented the true cinematic sound experience.

6.1 Channel Setup
As you would expect the 6.1 speaker system adds an extra speaker to the 5.1 model. This speaker is the rear speaker. In the 6.1 setup the rear speaker is positioned directly behind you.

7.1 Channel Setup
Again the introduction of another satellite speaker is required when using the 7.1 speaker. This system gets rid of the centre rear speaker and replaces it with two rear surround speakers.

New Adventures in Hi-Fi
This hi-fi a& Computer audio article from cuts through the tech-babble and tells the story of multi-channel audio, and details the latest 'high resolution' surround sound formats.




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