Home Theater Audio Formats
Making sense of surround sound audio formats
It can be confusing trying to understand all of the Home Theater audio formats available. Just when you thought that all you needed was a good surround sound receiver and a few extra speakers to get into Home Theater, the guy at the store is laying all this extra stuff like DTS and Dolby Pro-Logic II. Let's try and make some sense of the formats.
Forward thinking audio engineers have tried to immerse audiences in sound since stereophonic sound was introduced at a demonstration at Carnegie Hall way back in 1940. The first widely used forms of surround sound were released in the 1980s during the boom of home video tapes on VHS.
Introduced by Dolby Labs, Dolby Surround was an acoustic algorithm that added an extra speaker behind the audience. All that was required was a stereo audio signal which most VHS tapes could produce when played through a stereo VCR and a receiver with Dolby Surround. The signal processor takes certain sounds from the two-channel audio signal and replays them with a delay through the rear channel. This is not a discreet channel, but simply a matrix of the stereo channels. The matrix technique would be used again anytime multi-channel audio is produced from a stereo source.
Dolby Pro-Logic was a slight improvement on Dolby Surround. Dolby Pro-Logic added a center channel designed to play the mid ranges that would playback the voices in dialogue sequences of films. The rear channel was extended to include a second speaker, but no significant additions to the content were added. Pro-Logic was still a matrix of the stereo signal.
Dolby Digital 5.1, originally known as AC-3, was the first discreet fully digital surround process. Things get really interesting with Dolby Digital and its ability to work six separate channels of discreet sound. Since each channel or speaker is discreet rather than comprised of a matrix of the other channels, each channel can play back an independent sound. The addition of a subwoofer or Low Frequency Effects channel makes the subwoofer an important player in any soundtrack. The LFE channel is indicated by the .1, meaning that it plays back one tenth of the audio information of the other full range channels.
DTS is a company that began creating an alternative to Dolby Labs digital effect processing since 1993. DTS soundtracks now appear on popular DVDs everywhere. They have been renowned for creating some of the finest soundtracks ever played back in home theater systems to date. Notable soundtracks done by DTS include Gladiator, Saving Private Ryan and Moulin Rouge. With a higher sampling rate than Dolby Digital and slightly more emphasis on effects, DTS has made themselves the audiophile choice for surround film enthusiasts.
Extended Formats: The extended surround formats include Dolby Digital EX and DTS ES; seven channel surround sound methods. They're really not much different from the 5.1 versions, but these add additional rear channel effects from back speakers that are to be placed behind the audience pointed at the audience's back rather than to the sides. These extra channels of sound are not discreet however and only a matrix of the surround channel information. This is why the extended formats are not considered true 7.1 or 8.1 surround methods; these are still only 5.1 digital audio formats. The only advantage to using the extended formats might be if you're using a very large room and need to fill in the surround channels with more kick.
Legend has it that the first extended surround format was thought up by George Lucas and co-developed by THX and Dolby Digital to produce Dolby Digital EX or THX-EX, which are interchangeable terms for the same format. Lucas was dissatisfied with the fullness of the surround channels and wanted more sound behind him. Most people probably aren't listening to movies in a Home Theater system the size of Lucas's, but if you think you might be, then by all means the extended formats probably have something tangible to offer.
Dolby Pro-Logic II and DTS Neo6: Two channel audio is alive and well in the digital music realm. As long as there are two channel sources feeding stereo signals into multi-channel receivers, there will be encoding formats designed to take advantage of all that extra hardware with which they're endowed. Dolby PL2 and Neo6 are just Dolby Labs and DTS's means of addressing this concern by offering processing to your two channel material that allows them to recruit the rear channels. They're strictly matrix methods like Dolby Pro-Logic, but a bit more flexible. They'll add a bit of dimension by taking from certain elements of the two channel information and playing it back in the rear channels.