Hotwired: Delivering digital sound for home theatre

To be fair, THX doesn't deserve its own Hotwired column but, with entertainment reporters all over the planet lathering over Revenge of the Sith, it is a timely opportunity to cover another George Lucas innovation.

Back in the late 70s, George realised he needed theatres showing his Star Wars and other such FX blockbusters to be able to reproduce the matching surround sound audio excitement as it was conceived and recorded in the studio. Knowing how bad some movie theatres sound even now, you can probably imagine how appalling most were back then.

Special-effects movies such as Star Wars can have literally hundreds of different sound elements in the soundtrack. Dialogue, sound effects and music are all separately recorded before being mixed down to a six- (in the case of 5.1) or four-channel soundtrack for movie theatre release.

By the early 80s, a range of standards and technologies for vastly improved cinema sound was developed from an ongoing research project dubbed THX, for Tomlinson Holman's Experiment - as well as reference to Lucas' 1971 film THX 1138 - Holman being the sound engineer employed by Lucasfilm Ltd to lead the necessary R&D.

Having established THX audio standards for movie theatres, the same thinking was applied in the early 90s to the new home theatre phenomenon. Six main requirements were identified: accurate frequency response; intelligible dialogue; full dynamic range; accurate on-screen location; smooth audio panning and an enveloping sound field.

THX electronic processing is intended to deliver digital 5.1 sound with cinematic realism. It includes trickery such as bass management, speaker time synchronisation and timbre matching. THX is not a process for getting more channels of audio information such as Dolby Digital, but rather an audio performance measure.

You'll find the distinctive rectangular THX logo on DVD players, amplifiers, receivers with digital 5.1 decoding, home theatre speakers and accessories such as cables and acoustically transparent projection screens. THX-certified products have passed a series of tests designed to ensure they measure up to Holman's experimental goals. Brands pay the royalty fee, have their products tested and become licensees of the logo for compliant models.

Turns out that the original home THX research and specifications were based around a 3000 cu ft (85 cu m) lounge area, which is on the grand side even for many American homes. In 1998, Lucasfilm launched a new set of standards for mid-priced receivers and speakers they called THX Select, with performance maximised for 2000 cu ft (57 cu m) rooms. The original, more luxurious spec was rebranded as THX Ultra.

Home theatre components bearing a THX logo basically guarantee the buyer they will meet a certain level of performance. It's a convenience and an assurance, but there are plenty of non-badged products out there that will meet or exceed THX standards - some manufacturers just don't want to pay old George for the use of his logo.

A THX-configured system will provide you with the means to ensure the best sound for your home theatre, though for most, it will simply be another logo paid for but unused. I'm sure George won't really mind.