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Understanding Surround Sound Formats
Confused about surround sound formats? Here's a guide to clear things up.
Let's start by defining some frequently used terms. You can also take a look at our surround formats chart.
5.1: 5.1 surround sound is the most common format. It includes a total of six channels — five full-bandwidth channels with 3-20,000 Hz frequency range for front left and right, center, and left and right surrounds, plus one "low frequency effects" (LFE) subwoofer channel for frequencies from 3-120 Hz.
6.1 and 7.1 surround sound systems are also available, and simply add another full-bandwidth channel to the mix. (To see how the speakers are arranged in a multichannel surround system, check out the diagrams in our guide to home theater speaker placement.)
Discrete: Some channels are considered "discrete" — that means that the sound information contained in each of the available channels is distinct and independent from the others.
Matrixed: Other channels are considered "matrixed" — that means that the sound information in those channels is extrapolated from information in other channels. Though you'll notice more precise surround effects from discrete channels, you can still expect engaging sound from matrixed channels.
Lossless: Some surround formats are compressed so that they're small enough to be stored or transmitted — on a DVD, for example, or in a satellite TV broadcast. But higher-capacity Blu-ray Discs™ can hold lossless surround soundtracks that are identical to the original studio recording. The higher quality of these formats makes for more detailed audio.
There are two main formats that deliver surround sound for 5.1-channel systems.
Unlike earlier forms of surround sound, Dolby Digital 5.1-channel audio is a discrete multichannel surround sound system. With six discrete channels, sounds can be placed very precisely, for improved dialogue clarity, imaging, spaciousness, and realism. You also get a dedicated subwoofer channel, for plenty of deep bass.
Like Dolby Digital, DTS® provides 5.1 channels of digital audio. However, DTS uses less compression than Dolby Digital. As a result, some say that the sound produced by DTS is slightly more accurate than the sound produced by Dolby Digital. While most audio/video receivers will have both Dolby Digital and DTS, fewer discs and video games are encoded with DTS, compared to the number encoded with Dolby Digital.
A 6.1-channel system uses a single rear surround speaker to deliver an even more enveloping surround effect.
DTS-ES™ adds a discrete, full-bandwidth back surround channel.
Dolby Digital EX and THX Surround EX
These formats add a matrixed back surround channel for a 6.1-channel speaker system.
Many DVDs are encoded for Dolby Digital EX, and have the extra channel of surround information ready to go. If you're playing a regular Dolby Digital 5.1-channel DVD, a Dolby Digital EX or THX Surround EX™ decoder will simulate 6.1-channel surround by processing the audio information in the discrete surround channels and sending the matrixed audio info to your back surround speaker.
Blu-ray players support 7.1 audio formats and high-quality, lossless surround sound.
While your high-def disc player and receiver may be able to decode these new surround sound formats, not all discs you play will take advantage of them. Be sure to check out the details on the Blu-ray discs you watch to see which audio format they use.
Lossless surround sound formats
Dolby TrueHD and DTS-HD™ Master Audio, offer up to 7.1 discrete channels of lossless audio. Along with adding two extra rear channels to the standard Dolby Digital and DTS formats, Dolby TrueHD and DTS-HD Master Audio discs are encoded with more audio information per channel. In fact, it's identical to the movie studio's original master. That means the improved directionality and more precise effects makes it even closer to the experience of being in a movie theater.
Additional discrete 7.1-channel surround formats
You may find that some Blu-ray discs are also encoded with other discrete 7.1-channel surround formats. Dolby Laboratories and DTS developed Dolby Digital Plus and DTS-HD (High Resolution), respectively. These formats deliver 7.1 independent channels of sound. They provide more detailed surround effects than 5.1 Dolby Digital and DTS, though they aren't lossless like Dolby TrueHD and DTS-HD Master Audio. Receivers that support lossless 7.1-channel formats will also support Dolby Digital Plus and DTS-HD (High Resolution).
"Height" channels for a taller soundstage
A few receivers offer a newer surround sound format called Dolby Pro Logic IIz. It adds two "height" channels to your front soundstage. These speakers typically mount on the wall above your existing front left and right speakers.
A receiver with Pro Logic IIz can divvy up the front soundstage audio. It sends directional sounds — like a car racing by — to your regular front speakers, and non-directional sounds — like the roar of a crowd at a stadium — to the height channels. The result is a larger, deeper front soundstage, and a more immersive experience.
Dolby Atmos® adds overhead sound to the mix
This innovative surround sound format uses in-ceiling or Dolby-enabled upward-firing speakers to project sound from above your seating positions. Receivers with Dolby Atmos capability can create an incredibly immersive listening experience by placing sounds more accurately in the room than conventional setups.
Dolby Atmos soundtracks use two distinct sound fields to achieve these effects. The "bed" consists of stationary sounds such as background sound and music. "Objects" are assigned specific locations in the three-dimensional listening space, which the in-ceiling or Dolby Atmos enabled "top" speakers help bring to life with depth and realism.
Matrixed surround decoding for older sources
If you use a stereo analog connection to your receiver, or are connecting older equipment like a VCR, your receiver may employ one of these types of processing to decode the signal. Dolby Pro Logic II includes two independent full-bandwidth front channels, three matrixed surround channels, and a dedicated low-frequency channel for your subwoofer. Many recent home theater receivers also offer Pro Logic IIx processing, which can turn the same sources into even more enveloping 7.1-channel sound.
DTS Neo:6 is essentially identical to Pro Logic II — it's simply the processing DTS came up with to deliver 5.1 or 6.1 channels of sound from a two-channel stereo source.
"My receiver has other surround formats, too"
Sometimes manufacturers will put their own special processing in a receiver, often called Digital Signal Processing (DSP), in addition to the formats described above. Many home theater receivers use Digital Signal Processing to create soundfields — simulated acoustic environments, like a concert hall or stadium — and for precise steering of multichannel soundtrack information. This feature may go by different names, depending on the manufacturer. Check your owner's manual for details about your receiver's DSP modes.