THX is the standard for the sound track, not for the sound formats as with Dolby Digital and DTS. Therefore, the two standards can be used simultaneously. If THX films recorded using Dolby Digital or DTS are played back with a Dolby Digital or DTS amp that uses the THX system, the result is even better sound effects. So in essence THX is more of a quality assurence program rather than a sound system.

The consumer format THX system incorporates the various techniques used in the theatre system so users can enjoy the full cinematic experience in their own home.

History of THX
The first movies were silent, with “talkies” introduced later. Cinemascope and stereo sound effects were subsequently developed, followed by the Dolby system featuring Surround Sound. Unfortunately, the sound systems of movie theatres lagged far behind those of these technologically advanced sound systems.

Lucas Film created a wonderful sound mix in the film “Return of the Jedi’ (of the Star Wars series). When the film was tested in an ordinary movie theatre, however, there were some sounds that could not be heard in the theatre but were audible in the dubbing studio. In order to make such sounds audible in the theatre setting as well, THX was developed. The name ‘THX’ comes from George Lucas’ film ‘THX 11 38′ and the X-over (cross over or crossover frequency filter) of the THX filter developer, Tomlinson Holman.

Onkyo 7.1 Home Theater

Configuration of THX
The THX Sound System has a variety of regulations involving the recording studios, playback equipment, theatres’ sound system and acoustic conditions, and other factors. Inspections to ensure compliance with these regulations are carried out every 6 months. However, at home, using only the THX processor and speakers for THX, you can enjoy the impact of THX sound. The THX system for home use is designed to be unaffected by the room’s acoustical characteristics.

	Yamaha 7.1-Channel Home Theater Receiver

Introduced in the movie ‘Jurassic Park’ in 1993, DTS features superior sound quality and reliability, and has expanded to general consumer use.

Consumer-format DTS is basically the same as that for theatre use, but the soundtrack is provided as part of the CD, LD or DVD, A DTS disk looks no different to any other disk. DTS and DTSes is currently the premium format for sound reproduction far superior than Pro-Logic and also slightly better than Dolby Digital.

DTS-ES (Extended Surround) is a newer version of the DTS format, it adds an extra speaker to the rear of your home theatre setup. Called a 6.1 setup it is compatible with the existing 5.1 media. Two variants of DTS-ES exist, one is known as DTS-ES Matrix as it gets the sound for the 6th speaker by matrixing the two rear speakers creating a rear centre speaker channel, While the other version is known as DTS-ES Discrete as it contains a complete 6th channel for the rear centre speaker.

DTS was expanded yet again around the time Blu Ray and HD DVD hit the market, now in a 7.1 format know as DTS-HD Master Audio and DTS-HD High Resolution Audio. The Master Audio version can be described as a lossless audio format where every part of the original studio recording can be reproduced in your home bit for bit. The High Resolution Audio version is not as perfect as the Master Audio version but your ears probably wont pick it. It is often used on Blu-Ray discs where space is limited to fit the Master Audio version. A DTS-HD amp will be compatible with both versions.

	Sony STRDG720 7.1 Audio Video Receiver

Now, there are a number of advanced technologies that significantly improve audio performance in movie theatres. These advanced technologies include Dolby Digital, DTS, and the THX system. As with most of the technology that was first seen in theatres, high tech surround audio systems can now also be enjoyed at home. There are a few formats on the market now that have developed as time goes on so in this series we are going to take a look at various surround sound technologies.

In a movie theatre viewed from above, you would find the speakers are arranged so as to surround the audience. Speakers are placed In front of the screen along the walls to the left and right of the audience and to the rear.

By contrast, at home it is not easy to arrange the same equipment in the same position as in the theatre because of differences in room size and layout as well as acoustical problems. The most popular layout is the 5.1 layout that usually consists of left and right front, centre, and 2 surround speakers normally placed near the rear. Hence the 5 for the 5 audio channels in the room, the point 1 actualy refers to the Low Frequency Effect (LFE) speaker also known as a subwoofer. Dolby Pro Logic II was the first system to use this format, the earlier Pro Logic system was known as a 4.0 system despite having 5 speakers as the rear surround were mono and it also lacked a subwoofer.

Dolby Pro-Logic was the first major step forward in home theatre systems it encodes a centre and rear channel in the existing analog audio tracks, a good effect could be achieved with a pro-logic amp. Today’s Dolby Digital and DTS systems use a totally digital signal to achieve 5.1 channels and are far superior.

All six speakers are controlled independently in the Dolby Digital and the DTS sound systems as apposed to the earlier analogue Pro Logic systems. There are even extensions to the two competing formats that see even more speakers added to your lounge room with 6.1 and 7.1 systems.

Most amps sold today are backward compatible, therefore if you purchase a DTS amp you will be able to play Dolby Digital and Pro-Logic signals as well as the DTS signals. In order to get the benefit of a Dolby Digital or DTS amp you will need a digital cable ran from your audio source, your CD or DVD play may have a single plug on the back labeled digital out or SPDIF next to the standard left and right cable. you will need to run this to you amp to benefit from digital surround sound. A Pro Logic system lacks this connection as it is a totally analogue system decoding the 5 channels from the left and right channels. With a digital surround system digital audio is fed from your DVD into your amp where it is processed into the separate channels.