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Feature Article

THX-Certification: What It Means and How to Use

January, 2006

Brian Florian

Introduction

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

Summary of content (15 pages)

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Feature Article THX-Certification: What It Means and How to Use It January, 2006 Brian Florian Introduction 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.
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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). In the years to come, Tom Holman was not idle.
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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.
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the WHOLE system is assured, without any "matching" effort required by you, the end user. THX controllers are a perfect match for THX amplifiers, end of story. You can think of this in terms of dynamic range windows: when they all line up, you get maximum performance all the way through. The second, somewhat distinct aspect of certification of a THX Controller is the inclusion and implementation of various design features, including the THX Post-Processes.
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formats, De-Correlation became Adaptive De-Correlation, intelligently applying itself when discreet surrounds contain mono content. the exact same signal. This can cause the sound to be "in your head" instead of pleasantly surrounding you as it should, or if seated off center, can cause the surround sound to collapse to the speaker nearest you.
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corresponds to reference level playback. In turning the volume down, the volume level is expressed in -dB, or how many dB below reference level you are. Separate Amplifiers and the Amplifiers in Receivers Metrics Tested on THX Amplifiers: It's too easy for people, including us here at Secrets, to say "get as much power as you can", "you should have at least 100 watts per channel", and so on.
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Starting with the more pedestrian facets of speaker performance, it almost goes without saying that THX speakers must have no compromise in terms of neutral frequency response, power handling, output capability, and the often overlooked dynamic, or transient, response.
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The THX crossover consists of an 80 Hz, 4th order Linkwitz/Riley filter alignment, and it was not chosen lightly or without serious consideration. As the crossover frequency increases, it becomes harder to blend the subwoofer with a satellite, and the subwoofer becomes more difficult to audibly "hide". At the same time, as the crossover frequency increases, distortion from the satellite decreases, the total dynamic range increases, and loading the room for the flattest response becomes much easier.
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THX dipoles must meet a strict requirement of flat total power output, which means the sum of the sound coming spherically from all around the speaker must be smooth, as opposed to the sound coming from just one of the poles. This is not easy for a designer to do, and there are plenty of examples of poorly designed dipoles (none of which are THX-Certified).
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Whereas THX/THX Ultra was specified and designed for rooms "up to" 3000 ft3, THX Select took that requirement down to 2000 ft3. Both the requirements of the amplification and the output of the speakers were scaled back appropriately, placing THX in the hands of a whole new audience who could not have otherwise afforded it. When it comes to amplification, continuous output tests are run on up to one, four, and five channels (simultaneously) of an Ultra product, but only one at a time on Select.
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music setups. This mode also disengages Re-Eq because music tends to be enjoyed at a lower median level than movies, and as such does not need it. THX Game. This mode basically puts all surround speakers on full duty, giving you a very lively, "exciting" sound experience which is what people want when playing an active video game. The THX Ultra2 Layout For THX Surround EX, ASA places "virtual" speakers in the requisite position.
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Its important to note that the Ultra2 controller has a setting for the distance between the two rear speakers, the default being <1ft as depicted above, yielding the most spacious sound field. The alternate setting of 1-4 ft can be used to "favor" the music playback mode. By moving the physical rear speakers apart, there is less of a "virtual speaker", with more of the surround sound in Music mode coming from the monopole rear speakers. Ultra2 Hardware THX Ultra2 also raised the bar for speaker performance.
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Benchmark. Composite and Y/C Chroma Delay Chroma Differential Gain Chroma Differential Phase Burst Amplitude Differential Flesh Tone Phase Error Luminance Linearity AM Chroma Noise PM Chroma Noise Chroma Correlated Noise (IM) Chroma Burst Frequency Leakage in Y Chroma Burst Frequency H Sync Timing Another THX product which leaves us scratching our heads is cables, and that's NOT a reflection on THX. It's no secret cables are a high margin item, but the THX cables we've seen take it to a whole new level.
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Design Manual for the product in question. THX products are designed to be THX products. The manufacturer knows what they have to do from square one. Once they have a working sample, it is sent to THX where it is tested, for a fee, and either checks out and a license granted, or it is sent back with a report on what needs to be addressed. THX tells us that they have yet to receive a product which got everything 100% right on the first try.
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performance-oriented presentation. For the first time, the person doing the raw art, sound bites, 3D environments, or what have you, can be assured that the effort they put into their work will be realized right to the end because everybody's workstations, environments, and equipment are all set up to the same consistent standards. Room acoustics, background noise, room lighting, every piece of audio and video equipment, all must meet certain THX performance requirements.