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 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.
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.
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.
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.
