Feature Article

THX-Certification: What It Means and How to Use It

Part I

January, 2006

Brian Florian



THX is almost a quarter century old, and its Consumer Branch has been around since 1990, yet people still do not have a proper understanding of THX.  Maybe that's THX's fault, maybe it's ours (the press), maybe it's the sales people's at the local A/V store.  Probably, it is a combination of all three, so we're going to at least do our part and tender to you, our readers, this explanatory article.

We will try and dispel the myths, reiterate the truths, and of course give you our slant on the whole thing as well.  If you think you know THX, you might be surprised at what you read here.  We're in for quite a ride, so let's get comfortable.

In the Beginning . . .

There is now an urban legend that George Lucas walked into a small town movie theater one day and watched Star Wars.  The sound system was so poor and so out of alignment that no one could understand the dialogue and the picture was a mess.  He decided then and there to found THX, a company which would push out to the world a standards based certification program for movie theaters so that artists could have confidence that their work was being presented as they had crafted it.

True story?  In essence at least, if not in fact.  Regardless, it's a cute fable which makes for a nice ice breaker.

No, THX grew out of the development of Skywalker Sound, the state of the art post production facility that George Lucas created with the profits from the first Star Wars.  Skywalker was to be (and to this day is) the high water mark for facilities of its kind.  In developing the the various setups for Skywalker, Tomlinson Holman and the Lucasfilm engineers, through experience and research, defined the ideal standard for mixing rooms, incorporating all the existing international standards set down by SMPTE, ITU, etc.  These became the very first THX standards.  The year was 1982.  When the word got about about just how good things were at Skywalker, the other studios in California asked if their facilities could be upgraded to the same standard.  The concept of being "THX-Certified" was born.

Once they started bringing other professional facilities up to their standard, THX realized that what they were doing could be "pushed out" to the local movie theaters, creating an end-to-end consistency in the way movies are crafted and then presented.   Everything from the light level on the screen, the background noise level in the room, the quality of the theater and all its equipment, even the quality of the prints and the consistency thereof come under the THX TAP, or Theater Alignment Program.  In 1983, the AVCO cinema in Los Angeles was the first theater to receive THX certification.

In the years to come, Tom Holman was not idle.  While listening to master tapes of film sound elements at home on top quality hi-fi gear, he and the sound designers and mixers weren’t happy, because the same tapes played in both spaces didn't "translate" accurately. This led Tom to the first set of specifications for THX consumer gear, which we will talk about at length in a moment, and the subsequent launch of the first THX home controller in 1991 (the Technics SH-THX10).

Myth:  "THX DVDs have THX sound on them which requires THX equipment to play."

Reality:  A THX DVD is one which has been mastered under their supervision to the industries highest standards.  There is no proprietary format or content.

As VHS, LaserDisc, and the whole home theater concept began to take hold, THX was approached to monitor the transfer of film to video.  In 1993 the THX Digital Mastering program was launched, providing the service of consistently applying the technologies and specifications of best-practice telecine processes (transferring the image from one medium to another: film to film, film to tape, film to computer, etc.)

A DVD which is THX Digitally Mastered is not technologically different from any other.  You do not need THX equipment to play the disc or realize some special feature on it.  THX Digitally Mastered simply means that the film has been transferred under technically correct and consistent processes.  In virtually every case the film's director, art director, or sound designer (or all three) are present and are free to make artistic choices, with THX's role being one of supervision, ensuring that those choices are being made under the correct circumstances and that they translate as the artist intended to end audience at home.

Quick sidebar:  In the time before DVD I had bought the VHS of James Cameron's Titanic.  It did not take long to realize the audio on the tape was reversed left to right.  I e-mailed THX and within a day I got a phone call asking if they could send FedEX to pick up the tape and drop off a replacement (along with a T-Shirt).  Being a THX Digitally Mastered title, they wanted the tape so that they could figure out exactly which duplication machine it was made on and correct it.  True story!

THX at Home

THX Home Cinema is fundamentally about one thing: The technically competent and correct reproduction of a piece of audio/video work.  Period.  THX is able to achieve this through a very precise, defined specification for hardware which goes well beyond conventional metrics, as well as the incorporation of proprietary technologies and processes that are integral to the system.  Their intention is to offer the consumer a system with baseline performance which closely replicates the monitoring environment in the studio. Once that baseline is in place, the consumer can change things any way they like knowing that they can always go back to a baseline that's pretty darn close to the original recording environment.

You may have read the usual diatribe about the goals of THX being:

Intelligible dialogue
Pin-point localization
Enveloping surround
Accurate frequency response
Generous dynamics, soft as well as loud
Accurate coverage ("Every seat is a good seat.")

Yawn!  That's all well and good, but frankly that should be the goal of ANY product which makes any sort of "hi-fi" claim (though achieved by few).  Performance metrics are obviously the heart and soul of THX certification, but the real benefit of THX for the consumer is exactly how these standards and design elements were arrived at.  Holman knew that the source tracks sounded different in a home space, despite him listening to them over absolute state of the art home systems of the time.  It would have been easy to say "lets just do the same thing we do at Skywalker sound", but that is utterly unrealistic, even for the very wealthy (and I don't know if this was on George's mind, but technically competent and correct presentation of movies should not have to be the province of millionaires alone).

So in addition to simply drawing on the technologies and specs already developed at SkyWalker for professional facilities, THX Home Cinema did something more:  They addressed the REALITIES of the consumer market.  They realized that consumers would not put wall-to-wall acoustical treatments in their home, or install an array of 12 surround speakers.  They realized that for the most part, home theater is "living room theater".  Even so called "dedicated" home theaters have more in common with living rooms than they do with Stage C at Skywalker.  As we'll see, everything about a THX piece goes back to this fundamental.

A few words on "Reference Level"

Before we start talking about the pieces and parts, we first need to take a quick refresher on the concept of "Reference Level", as you are going to be hearing that term quite a bit in the coming paragraphs.  Simply stated, Reference Level is a standard, known, predictable and reproducible playback volume level.  When movie sound tracks are crafted, they are done so on systems which are locked at this level.  The sound artist does not play around with a big volume knob when doing his/her work.  If the sound artist wants something to be loud, they make that sound loud within the sound track.  When they want something to be soft, they make that element soft within the sound track.  Movie theaters set their playback level by the exact same rules, so when the movie is shown, you hear EXACTLY what the sound artist heard when they were making the piece.  Loud, soft, in-between, it's all there, and no one touches the master volume knob over the course of a two-hour movie.

To achieve THX certification, components must play at this reference level without breaking, distorting, buzzing, rattling or any other distracting effects.

Reference level is by any definition, objective or subjective, quite loud.  It basically mirrors the dynamic range of the studio system, which in the case of all movie sound tracks, is 105 dB.  Any single channel of the system is calibrated to play 0 dB FSD (the loudest sound the sound track can contain) at 105 dB (115 dB for the LFE channel).  While that is really, REALLY loud, its important to remember that there is 105 dB of dynamic range and the artist can put a sound at any level they want.  So while a system's volume may be set to reference level, dialogue within the sound track can, and most often is, at a normal, natural level.  Reference level, with the dynamic range available, permits a movie to have that normal, natural dialogue, and then suddenly a spectacular, loud car chase without anyone touching the volume control.  Every element in the sound track comes out as it should.

Now, having said all that, watching a movie at reference level in a home theater is almost never done.  It can be extremely loud to begin with, but the close spaces typical of home theaters make it perceptibly even more so.  Reference level is still very important in home theater though for several reasons.  Because it is the absolute loudest a sound track should ever be played, its fairly intuitive that its a good idea to have a system that can competently go that loud.  It gives you a sort of "safe maximum" volume level, even though you may never push it that high.  Even more important though is knowing what volume you are at RELATIVE to reference level because if we go too low, we literally lose the quietest sounds since they are pushed below the audible threshold, surrounds lose their presence, the perceived spectral distribution of the track is altered, and dialogue intelligibility suffers.

Click Here to Go to Part II.

© Copyright 2006 Secrets of Home Theater & High Fidelity

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