In this hopefully informative article, I will be looking at the many different current Surround Sound formats available to consumers. I will cover Dolby Surround, Pro-Logic, Dolby Digital, DTS, THX Surround EX, DTS-ES (and DTS-ES Discrete), Pro-Logic II, and THX. If you are confused by all these sound formats and wonder what is best for you, or what your current system can handle, with any luck this will be of some help.
Dolby Surround and Dolby Surround Pro-Logic™
Dolby Surround Pro-Logic has been around since the early 1990s. Its popularity as a format is most likely due to the fact that it can be encoded in standard stereo channel; therefore, it is the standard for TV broadcasts and HiFi VHS. Pro-Logic encodes four channels, left, right, center (discrete), and rears, whereas standard Dolby Surround has a phantom center channel that is derived from the left and the right. Dolby Pro-Logic also does a better job of addressing directional sound, amplifying certain channels over others to derive believable movement. Pro-Logic does leave a lot to be desired though in the terms of creating a truly surrounding experience, as even though there are two rear speakers, they are both playing a mono signal. Dolby Pro-Logic receivers can work fine with your DVD video discs, because all players will down-mix Dolby Digital into Pro-Logic via their stereo outputs.
Dolby Digital (a.k.a. AC-3) is, for the most part, the de-facto sound standard of most newly released DVDs. Dolby Digital provides 5.1-channel sound, or sound to up to five discrete channels, and a channel for low frequency effects (LFE) for your subwoofer. The 5.1 classification is due to the fact that the five independent channels are capable of receiving theoretically full frequency sound (20 Hz to 20kHz), thus 5, and since the LFE channel only receives the much lower frequencies (20 to 120 Hz) it gets the .1 label, thus 5.1. This being said Dolby Digital does not require all six channels to be used, rather it can be tailored to the producer; some other flavors you might see are Dolby Digital 1.0 (mono), Dolby Digital 2.0 (stereo, Surround, Pro Logic), etc…
To actually be able to use Dolby Digital your receiver must support it, in which your DVD player would output the AC-3 bit stream digitally to the receiver’s AC3-in, or your DVD player must have a built in Dolby Digital decoder and a receiver that is labeled as being Dolby Digital ready. Older Pro-Logic receivers will not do it.
DTS Digital Surround™
Digital Theater Systems Digital Surround is the competing 5.1 format to Dolby Digital. DTS is very similar to Dolby Digital in that it provides up to 5.1 surround sound like Dolby Digital and provides the same frequency levels to each channel as Dolby Digital. The difference between DTS and Dolby Digital is that DTS allows for higher data rates (1.5 Mbit/sec or 754 kbit/sec) in encoding its 5.1 audio tracks, two to four times the data rate compared to Dolby Digital. Because of this one could easily conclude that DTS is up to four times less compressed and can therefore sound better then Dolby Digital. DTS is slowly catching on, most likely due to the newer 754 kbit/sec data rate spec, which allows companies to place both a DTS and Dolby Digital track on their discs.
Again, to be able to use DTS your receiver must support it and your DVD player must be able to output it (look for a DTS sticker), or your DVD player must have a built in DTS decoder and a receiver that is labeled as being DTS ready.
THX Surround EX™
THX Surround EX, created in conjunction with LucasFilm-THX (Star Wars: Episode 1 The Phantom Menace is the first DVD to use this technology) and Dolby Labs, is very much based on the existing Dolby Digital 5.1 technology. The one drawback to traditional 5.1 Dolby Digital is that movement from left rear to right rear or vise versa can sometimes be unconvincing as their really is no intermediary between the sound. This is where THX Surround EX comes in, incorporating an additional channel: the rear center. Because this format is based on 5.1 Dolby Digital, it is only logical to assume that this rear center channel cannot be a discrete channel, and instead is matrixed from the rear left and rear right sound, thus not making it completely true 6.1, but close to it. In order to take full advantage of this THX Surround EX one will need a THX Surround EX capable receiver.
DTS Extended Surround and DTS ES Discrete 6.1
DTS-ES is Digital Theater Systems’ attempt at 6.1 surround sound. DTS-ES is very similar to THX Surround EX in that the rear center channel is matrixed from the rear left and rear right. DTS-ES Discrete, on the other hand, provides true 6.1 Surround Sound by adding a truly discrete rear center channel, making it the only surround format that is actually 6.1. To take advantage of these formats your receiver will need to be, you guessed it, compatible with DTS-ES and/or DTS-ES Discrete.
Dolby Surround Pro-Logic II™
A new format on the block, Dolby Surround Pro-Logic II is the next step in Pro-Logic sound, attempting to liven up previous Dolby Surround tracks by creating a fresher ”5.1-Like” experience. Dolby labs is quoted saying on this new technology, “Pro Logic II was designed from the outset to convert conventional stereo music recordings, which will be with us for some time to come, to a natural, believable surround experience. The result is a decoder that can handle a wide range of movie and music program material with equal skill.” Obviously, receivers that are strictly Pro-Logic II capable (and not Dolby Digital also) are targeted at the lower end audience, but whereas receivers with the full array plus this new format would be available for the extra cash. It will be interesting to see how this format does, as it could theoretically make for decent simulated 5.1 Surround sound from current CDs and movies. As a side note, Pro-Logic II is also being used in some games for Nintendo’s new GameCube console. Pro-Logic II makes sense in this kind of a situation in which sound is unpredictable, rather then Dolby Digital, because of the latency involved with encoding Dolby Digital on the fly (50-100ms), whereas creating a 5.1 Pro-Logic II environment has zero overhead and therefore results in a truer surround experience that does not seem slightly delayed.
The THX certification does not really fit into this article very well, as it is not a surround sound format; rather it is more of a quality control label, guaranteeing “THX quality” video and sound. This is a certification given by Lucas Films Ltd., which implies that a given DVD audio track’s quality reaches their standard for optimal surround sound performance. Theoretically, to fully achieve THX quality sound, your entire system will need to bear the THX logo. You may also see the THX Ultra and THX Select certification, implying higher and higher standards that are held to various audio components
What does the future hold for Surround Sound? 6.1 and 7.1 will become more standard and more used. Less lossy formats (less compression) will almost certainly come soon as DVD discs are tapped for all the space they can offer. One must face that fact that any top of the line receiver they buy now will not be so the next year, it is just the way technology evolves. Buy what you can afford and what fits your needs. Not everyone needs true 6.1 - or do they? :)