It might seem like standards soup, but the sheer variety of standards for listening to surround sound audio can make your head spin. While each one has a specific purpose, home theater buyers need to worry about a few specific standards, and then likely can ignore the rest. We'll explain exactly how each standard differs, and the ones that are most important to your surround sound system.

Back in the early 90s, two companies started working on competing standards to extend audio past simple two channel stereo audio, and into full on immersive surround sound. Starting with Batman Returns in 1992, audiences were treated to the first 5.1 surround mix in Dolby Surround sound. Competing company Digital Theater Systems (DTS) released its first film the next year with 1993's Jurassic Park.

The main difference between the two systems is how the formats are delivered to theaters, and not how they're delivered to homes. Individual theater owners have the option of opting for Dolby, DTS, a format from Sony, or using the analog tracks included with the film. In the picture above, all four formats are represented as part of a film reel. The left most format, in blue, is Sony's SDDS format. To the right of that is Dolby Digital, represented with the Dolby logo in the center. Next is the film's analog audio track, and to the right of the analog audio are little white markings which represent the timecode for DTS. DTS is actually distributed on a separate CD with the film, instead of being printed directly on the film.

Now that we've touched on surround sound in the cinema, lets talk about surround sound where it counts: The home theater. Obviously, all the audio formats are distributed with the film on a DVD or Blu-ray disc, so there's no semantic debate about ease of distribution, so what's the big difference between Dolby and DTS? In practice, not much. The two vendors distribute different versions of their surround encoding and each one has its own advantages and disadvantages for content producers, but the end result in your home is largely similar.

Dolby

The first into the surround sound scene is also one of the most widely used vendors. Dolby set the bar by being first out of the gate, and the company hasn't exactly slowed down. With more incremental formats than DTS, Dolby's naming scheme gets a little bit confusing, but it's pretty simple once you understand the bigger buckets the formats fall into. Oh, and Dolby has 13 other formats we didn't mention that are safe to ignore.

Digital and variants

Dolby's original surround sound format, called Dolby Surround, was an analog format (for more, see Pro Logic below) and Dolby Digital was the company's foray into home theater digital audio. Dolby Digital has five discrete channels of audio, meaning each part of a surround sound system is encoded separately from the others. To fit the audio on a DVD, Dolby Digital discards some of the audio information (lossy compression) and keeps the most important parts to be played back. Dolby Digital is one of the most popular formats for 5.1 audio and is included on most DVD players.

Apart from the original Dolby Digital format are a wide variety of variants. Dolby Digital EX adds faux 6.1 or 7.1 surround sound into the mix. Why faux? Unlike Dolby Digital, which has 5 discrete channels, Digital EX uses a sound matrix technology to extract the 6th or 7th channels from the existing five channels of audio, making it "pretend 7.1" in our books. I'm sure it sounds fine, but it isn't true 6.1 or 7.1 and if you're paying extra, you'd expect to get the true experience.

Dolby Digital Plus, sometimes referred to as AC-3, is the standard for digital TV surround sound distribution. Digital Plus is also one of the formats for Blu-ray discs, and offers up to eight channels of lossy audio.

Pro Logic II/IIx

Pro Logic II is an antiquated standard that was the original method for taking audio from two channels and presenting it in surround sound. Pro Logic uses a matrix technology to extrapolate a 5.1 (or 7.1 in the case of IIx) surround mix. Pro Logic is supported by virtually every piece of home theater equipment to be released in the last 10 years.

TrueHD

Dolby's next generation audio codec is called TrueHD. Instead of shoehorning audio into some sort of lossy encoding, TrueHD offers audio at 18 megabits per second, at full 24-bit / 96 KHz resolution. Basically, TrueHD aims to reproduce the entire soundtrack of a film at the same quality as the original master recording. Dolby TrueHD offers eight tracks of audio on Blu-ray discs, though the codec is capable of an unlimited number of tracks. Finding a TrueHD receiver will cost some extra money, but home theater nuts won't be able to find a better encoded audio signal.

DTS

The Pepsi to Dolby's Coke, Digital Theater Systems, or DTS, is the other notable surround sound encoding company. DTS doesn't have the number of standards that Dolby has, instead offering fewer standards that we find less confusing.

Digital Surround

DTS Digital Surround is the primary audio format produced by the company. While not inherently defined as 5.1 surround sound, typically the DTS Digital Surround designation means a user can expect a full five-channel experience. Like Dolby Digital, DTS Digital Surround is a lossy codec that throws out some of the information to squeeze it onto a DVD. DTS Digital Surround is much more common in current generation DVDs than it was in the early days, mainly because of the advent of a lower bitrate form of the codec. Originally, DTS films wouldn't contain very many special features because DTS audio was so large. Now, however, DTS audio is much smaller, allowing for a variety of audio formats without ditching the special feature content users expect.

96/24

While the name might be a little more cryptic than other branding, DTS 96/24 audio is a higher quality form of audio that's stored on DVDs. DTS 96/24 means that a DVD contains five audio tracks at a frequency range of 96 kHz and a bit depth of 24-bits, as opposed to simply two tracks. Instead of having to choose between surround sound or higher quality audio, DTS 96/24 is a crossroads of the two.

HD Master Audio

DTS-HD Master Audio is the counterpart to Dolby's TrueHD format. DTS-HD Master Audio is one of the formats compatible with Blu-ray, and like TrueHD, is only limited to 8 channels by the actual Blu-ray standard. DTS-HD MA can encode tracks up to 24.5 megabits per second, six megabits higher than TrueHD, and can easily be downmixed to 5.1 or stereo audio. DTS-HD's aim, like TrueHD, is to reproduce a lossless version of the film's original soundtrack.

Which format is for me?

The real question isn't which individual format is right for a home theater buyer, but instead how much can buyers afford to spend? Most DVD players and receivers will support Dolby Digital and DTS Digital Surround, however users looking for the extended functionality of DTS-HD Master Audio and Dolby TrueHD will need to expect to pay more for the privilege. Personally, I'm of the opinion that most current home theater buyers can be happy with simple 5.1 surround sound through either Dolby Digital or DTS Digital Surround. Most receivers support both standards, and 5.1 systems can offer a good value. 7.1 systems on the other hand are still seen as "luxury," and will have higher prices for less dramatic returns on investment. Find a system that supports Dolby Digital and DTS Digital Surround, and you'll be at a good starting point.

Have any other questions about surround sound we haven't yet covered? Be sure to send them in via our tips form, or leave a comment on this post. Oh, and don't forget to check out our other articles on surround sound basics and hooking up a home theater.

[Image: William Hook]