Comparing Surround Sound Formats

One of the most important parts of a home theater system is the sound -- that is, the surround sound.

While you probably know that surround sound involves the use of multiple speakers spread around the perimeter of your home theater room, you might not be aware that there are several different types of surround sound technology available today.

Dolby Pro Logic, Dolby Digital, DTS -- all the different formats can get a bit confusing.

Fortunately, most audio/video receivers contain multiple surround sound decoders, and handle all the format-switching automatically. But it still helps to know what you're dealing with -- so read on to learn more.

Matrix vs. Discrete Surround Sound

In the early days of home theater, surround sound was provided by analog matrix technology, as represented by the Dolby Pro Logic system. This type of surround sound system works mixing (matrixing) multiple surround channels into two main channels. The matrixed information then has to be decoded into the original channel configuration.

A better way to approach surround sound is to use digital discrete technology, like that used in the Dolby Digital and DTS formats. This type of surround sound system keeps all the channels separate from start to finish, producing a more clearly isolated surround effect.

While matrix technology has become more effective over the years, it's still not as realistic as discrete surround. For that reason, you'll find most current DVDs and all HDTV broadcasts encoded in discrete surround sound. Matrix surround is limited to older DVDs and to standard definition television broadcasts.

The First Surround Sound Format: Dolby Surround

Sophisticated Matrix Surround: Dolby Pro Logic

Simulated Surround: Dolby Pro Logic II

A Competing Matrix Format: DTS:Neo 6

Discrete Surround Channels: Dolby Digital

Dolby Digital + 2: Dolby Digital EX

An Alternative to Dolby Digital: DTS

Discrete Rear Channel Sound: DTS ES

High-Definition Surround Sound: DTS-HD

There's a new generation of high-definition DVDs on the horizon, represented by the competing Blu-ray and HD DVD formats. These formats are spec'd to include higher-quality surround sound than is available with either Dolby Digital or standard DTS.

The first of these high-definition surround formats is DTS-HD. This format offers lossless encoding and an unlimited number of surround channels. (Lossless encoding means that the audio tracks are offered with no compression, for the highest possible fidelity; it also requires a tremendous amount of bandwidth or disk storage.)

HD Surround from Dolby: Dolby Digital Plus

Of course, Dolby Laboratories is also getting into the high-definition surround sound market. Their Dolby Digital Plus technology is designed for use with both next-generation DVDs and high definition television broadcasts. Unlike DTS HD or Dolby TrueHD, Dolby Digital Plus does not use lossless encoding -- just a higher bitrate than used in regular Dolby Digital. It also supports up to 13.1 channels of audio in a single stream, although only 7.1 channels can be used with either Blu-ray or HD DVD discs.

Even Better HD Surround: Dolby TrueHD

Finally, Dolby has developed an even higher resolution surround sound format, similar to DTS HD, for use with the Blu-ray and HD DVD formats. Dolby TrueHD provides lossless encoding for higher fidelity across 7.1 discrete channels. As with DTS HD, this format is transmitted only when you're using HDMI connections.

Which Surround Format Should You Use?

In most instances, you listen to whatever surround format is encoded into the program you're watching and listening to. So, for example, if you're watching a movie on broadcast TV, you'll probably use Dolby Pro Logic IIx to listen to the matrix surround soundtrack. And if you're watching an HDTV broadcast, you'll use Dolby Digital in either 5.1- or 7.1-channel surround. But what do you do if you have a choice -- for example, if a DVD comes with both Dolby Digital and DTS soundtracks, as well as a Dolby Pro Logic soundtrack? First of all, always go with the discrete soundtrack, which means choosing Dolby Digital over Dolby Pro Logic. And if you have the choice, choose DTS over Dolby Digital, as it offers a higher bitrate and slightly better sound.

As to the next-generation surround formats -- DTS HD, Dolby Digital Plus, and Dolby TrueHD -- that's a decision for the future, as few current Blu-ray and HD DVD discs are encoded in these formats. (You're more likely to find a standard DTS or DTS ES soundtrack, instead.) In addition, audio/video receivers with next-generation decoders have not yet hit the market. Wait awhile for the marketplace to catch up with the technology, then go with the best format available to you.

Michael Miller is a writer and commentator on technology and digital lifestyle topics.