written by Mike Shea on 2 October 2000
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Among the most confusing elements of home theater, the subject of audio decoding methods stands the tallest. The market hype of the home theater industry will try to sell you on dozens of different "standards", but only a couple of them are really important when it comes to the quality of your home theater. If you are new to home theater and need an objective guide to the different audio formats, this article is for you.
There are basically three formats on the market right now that are of significance. Dolby Pro-Logic, Dolby Digital and DTS. You will find these logos on the front of many receivers and DVD players alike.
Dolby Pro-Logic. is probably the oldest of the true audio decoding schemes. Also known as Dolby Surround, this audio format takes a normal stereo signal and split it to include the center and surround channels. Because of the backward compatibility with original two channel sound, Dolby Pro-Logic is the most widely used but the least powerful of all the surround sound decoding methods. Originally receivers included this for a high price, but now every home theater receiver on the market includes Dolby Pro-Logic. For a more detailed look at this format, see the Dolby Pro Logic homepage from Dolby.
Dolby Digital 5.1 is a new format that has become more popular with the coming of DVD. This audio format offers any number of dedicated channels up to five main channels and one low frequency effect channel. Dolby Digital is the most popular current decoding method for DVDs and offers the following improvements on movie soundtracks:
If you are buying a new home theater receiver, make sure it includes Dolby Digital 5.1. For more information on purchasing home theater equipment, see the Home theater 101 guide, the Home theater for Cheap guide.
DTS is a competitor of Dolby Digital. It also offers a five channel plus low frequency effect channel, but it is not compatible with the Dolby Digital soundtrack. The marketing babble that comes out of DTS says that it uses a lower form of compression which gives you a better overall sound for your movies. I personally have not found this to be the case. Listening to both DTS and Dolby Digital versions of the film gave me little sense that one was better than the other. Dolby Digital or DTS can both sound excellent or shoddy depending on the quality of the soundtrack. Regardless, I certainly recommend getting DTS compatible equipment for both your DVD player and your receiver since the cost is minimal. Many DVDs now come with both Dolby Digital 5.1 soundtracks and DTS 5.1 soundtracks, letting you pick the version to listen to. One interesting side note, Dolby Digital includes a signal compression feature for late night viewing that DTS does not. This allows you to hear dialog and quiet scenes at their normal volume while louder scenes are suppressed.
No home theater trend is more misunderstood than THX. THX is a seal of approval for equipment and software, but not a particular decoding algorithm like Dolby Digital or DTS. There are detailed technical specifications applied to equipment or software in order for it to be THX certified. When you buy a THX certified piece of equipment, you are guarenteeing that this piece of equipment meets the THX standards. Here's an example of the specifications:
It is important to realize that there are many pieces of high quality equipment that do not meet THX standards. For example, the Skywalker ranch sound studio uses non-THX certified B&W 802 speakers to monitor THX certified recordings. THX certification is not something that one should require when purchasing equipment. Because of the high cost, I do not recommend the purchase of THX certified equipment.
Recently, Lucasfilm created a new lower standard for equipment known as THX-select and renamed the original standard to THX Ultra. The only difference between the two specs is the size of the room.
Recently, there has been two new formats, Dolby Digital EX, and DTS-ES. This decoding method first came to light with the theatrical release of Star Wars Episode 1. Immediately, the home theater industry spoke up about this format. Many home theater enthusiasts complained about the need to purchase new equipment while the industry started making "EX Compatible" equipment. DTS jumped on board with DTS-ES, a similar effort.
This decoding method works by taking the two rear channels of a Dolby Digital 5.1 soundtrack and run them through a Dolby Prologic-like decoder. This builds a third channel of sound from the two surround channels, which is sent to one or two amplifiers and speakers positioned behind the primary viewing position.
A few new receivers and decoders are hitting the market with Dolby Digital EX and DTS/ES decoding as well as some newer DVDs.My recommendation is to only include Dolby Digital EX as a required feature on receivers above $700. While it is still not a full requirement for a good home theater, more and more DVDs are including rear center channel information.
Within this plethora of acronyms, there are only a couple that are important when purchasing a home theater system. Dolby Digital 5.1 is the most important multi-channel decoding scheme used today for DVDs. Make sure whatever receiver you get has the ability to natively decode Dolby Digital 5.1. DTS is the second most used format, and it is cheap enough to purchase equipment with DTS compatibility that it is worth getting. DTS ES and Dolby Digital EX are becoming more popular but mainly for more expensive receivers. They are not required but if you can afford them, they may be worth getting.
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