THE THX FACTOR by Peter M. Bracke

"THX is like the Good Housekeeping Seal of Approval. It certifies that the product performs to a rigorously high standard that makes sense. THX provides the confidence and reassurance a consumer needs in a purchasing decision."

-- Promotional quote from the THX web site (Steve Baker, V.P. Sales & Marketing, Denon Electronics)

With the success of THX and the Theater Alignment Program in the 1980's, Lucasfilm began to refocus their attentions towards the reproduction of the theatrical experience in the home. But they soon found that the gulf between these two environments was considerably wider than that between the dubbing stage and the theater. The increasingly wide array of equipment choices open to home theater consumers, and widely varying quality of individual components, only exacerbated the problem. So with the goal of creating a program that would achieve the same high standards for home audio and video reproduction as TAP did theatrically, THX introduced the Home Theater Program in 1990.

In part two of our three-part look at the THX story, we will take a brief glimpse at at the Home Theater Audio program, and then a more in-depth technical look at the Laserdisc Mastering Program, which provides the foundation for the DVD Digital Mastering Program discussed in part three.

The Home Theater Era

The task of creating a workable set of standards for the home was considerable. Unlike in theaters and recording facilities, where comparable professional equipment is used in both environments, consumer electronics products are designed for audiences with much smaller budgets and acoustical spaces to consider. To surmount these obstacles, THX first defined what they considered to be the three basic parts of the home theater: the video delivery system, the audio delivery system, and the software itself. It was clear that if any one part of the chain was weakened , the entire home viewing experience would be compromised. Starting with the audio delivery system first, and set about to solve two key problems: correct the noticeable tonal and spatial errors caused by the discrepancies between large theatrical environments and smaller home theaters, and fulfill the need to reproduce the multi-speaker and complex sound fields created by extensive theatrical multi-channel sound playback.

After nearly four years of research into these areas, the core of the THX Home Program was solidified. It refined several key essential areas of home theater reproduction, including re-equalization of the sound mixing discrepancies between environments, "timbre matching" to compensate for the reduced number of surround speakers in home theaters, and improvements in front and rear dispersion methods to better increase the "hot spot" (ideal listening area). Perhaps most notably, and controversially in some audiophile corners, THX championed dipole speaker technology which diffuses sounds from the rear instead of utilizing more focused (and therefore more easily "localized") bipolar speaker designs (which were reserved fro the front speakers). This followed the foundation laid by Tomlison Holman in his initial recommendations for the TAP theatrical program, which favored disperse surrounds to increase the ambient soundfield, as opposed to advocating "hard" directional surround effects. THX also contributed to the advancement of subwoofer technology by setting standards for electronic crossovers, including peak bass level management and other guidelines.

Upon the introduction of the Home Theater Program to the marketplace in 1990, THX licensed its patented home theater program to a variety of audio/visual manufacturers, including Denon, JBL, Kenwood, Meridian, Pioneer, Runco and Technics. The full spectrum of consumer electronics products were covered, including Laser Disc players, receivers, power amplifiers, speakers, subwoofers and various system accessories (cables, equalizers, projection screens, etc.). The THX logo quickly became ubiquitous and synonymous with quality, and the THX Home Audio Program was off and running.

Though a major success, there still seemed to be one piece missing on the audio side: a standardized delivery method for discreet multi-channel surround sound. Thus, more research began and within short order Dolby Labs (in association with THX) debuted the first 5.1 (six channel) digital surround sound format in 1994 at the Consumer Electronics Show. Originally named Dolby Digital AC3 (which would later simply become Dolby Digital 5.1), the format was eagerly adopted by a home theater market that had long grown tired of the limited abilities of Dolby Pro-Logic (see Part One for more on the history of 2-channel matrixed surround sound).

However, backtracking to a year earlier, 1993 to be exact, with the home audio program a success, and it was time to move forward yet again, onto setting standards for the wildly inconsistent home theater software market.

The Laserdisc Mastering Program

With the announcement of their new Laserdisc Mastering Program, THX patented comprehensive new quality control services for the complete laserdisc production chain, from selection of source materials and the film-to-tape transfer (or telecine) process, throughout the complete replication and duplication phases. Tomlinson Holman and his team of associates focused their energies on ensuring that what the best audio and video quality format at the time, Laserdisc, would receive a comprehensive and rigorous set of quality controls. However, with digital technology already making inroads by the turn of the decade (with such pioneering features as The Abyss and Terminator 2), the choice to undertake a software certification program was also premeditated effort to prepare for future delivery methods. As Holman recently stated, "though laserdisc had its deficiencies in certain areas, it was a good launching pad to become prepared for the arrival of DVD, which was already being developed at the time." In addition to ensuring higher quality for the laserdisc format, THX was also laying the groundwork for the eventual DVD certification program and any future digital delivery methods (these issues are discussed further in part three).

Following months of development, the first THX "test discs" were produced, including Apocalypse Now and the Indiana Jones Trilogy (all of which were supervised and utilized parts of the THX laserdisc mastering program, but were not officially certified). Soon thereafter, the first THX-certified laserdisc debuted in 1993, James Cameron's extended cut of The Abyss. The response was positive overall, and major studios such as Twentieth Century Fox, Warner, and Universal, amongst others, were quick to utilize THX's services over the next several years. The THX logo soon became well known in the video market, and once again THX seemed to achieve the same success they had enjoyed back in 1983 with the Theater Alignment Program.

An Overview

The THX Laserdisc Mastering Program begins with the accumulation of the source materials. The best available elements are obtained, and the talent is consulted to assess their quality, as well as discuss any changes from the theatrical presentation that may need to be made. It is taking time out to note that the exact reproduction of the visual and aural components of a film for the home screen is impossible, just by the nature of the differences between the delivery medium and equipment. On the video side, issues of color correction, saturation and contrast, as well as compensation for deficiencies inherent in the NTSC video format, all have to be addressed, In the audio realm, matters such as the improvement in film sound over the past several decades often result in the Laserdisc being superior to the original source, thus necessitating discussion on whether to upgrade soundtracks for increased performance, at the expense of faithfulness to the source. Thus, numerous decisions have to be made that could alter the original content in order to maximize quality in the home. Further, often the talent involved is unavailable or deceased, making judgments on what the intention of the filmmaker originally wanted hard to ascertain. Needless to say, there has been, and always will be, debate and controversy about changes that are made, even the subtlest of ones, to the look and sound of the film when it is transferred to video.

But, significant alternations from the original theatrical presentation can be made in the video and audio, and this will not preclude THX certification. The stated goals of the program, to ensure the most faithful reproduction of the theatrical presentation as possible, would seemingly contradict the other stated goal of the program, which is to best reproduce the intent of the filmmaker. For example, though the majority of the THX laserdisc releases were in the aspect ratio of the original theatrical release, some "pan & scan" (cropped and altered) or open matte versions of films have been THX certified. However, again, THX works in consultation with the filmmakers, and serves their vision. For example, THX certified the James Cameron-approved full frame releases of The Abyss and True Lies, as well as their widescreen counterparts, which approximated their original theatrical presentations. The utmost goal of THX is to realize the vision of the filmmakers, even when they request to alter considerable elements of the original work. On the positive side, this affords filmmakers an opportunity to fix any elements that were lacking in he original presentation, and many time budget and time constraints resulted in deficiencies in the original. Still, the line between serving the filmmaker and preserving the original theatrical experience will continue to be a difficult and controversial issue. (A more in-depth analyses of creative decisions made during the initial stages will be discussed in part three of this article.)

Once the source elements are gathered and creative decisions made, the film to tape transfer is begun. THX personnel calibrate the viewing monitor utilizing a (rather scary-sounding) instrument known as the "Photo Research Spectra-Radiometer." Color, greyscale, black level, contrast and other factors are adjusted for optimum performance. This ensures that the best visual judgments can be made, as there is no will be no other video reference available during the process. The viewing window thus must be precise to afford the filmmaker the most accurate tool in which to properly reproduce the intended look of the film. THX also calibrates the dubbing machines, and uses THX-certified equipment in the the mixing process. Factors such as frequency response, phase modulation and level matching are all accounted for and inspected before any recording is begun.

Once the telecine is completed and synchronization between audio and video maintained, a D-1 Component Master (a high-quality digital master copy) results. THX then applies their patented video and audio test signals to this new D1. These signals are then copied intact to the subsequent NTSC master (called a D-2), and then transferred again to the actual physical disc pressing masters, and then again to the final replicated discs.

Though I will try to avoid becoming overly technical, the embedding of these test signals (patented waveforms) is accomplished by using the "vertical interval" in NTSC video. This is an invisible line between every frame, in which the signals can be continuously stored. Thus, every master and subsequent copy can be compared to each other during all stages of the process via these embedded signals. This ensures that quality is maintained between the original master and the final end product. (Note that when the D-2 master is transferred to the laserdisc pressing master, the digital source must be converted to analog, as laserdisc is an analog format. However, the test signals remain intact during this conversion.)

The embedding of these test signals is a key component of the THX mastering program, and every THX-certified disc has them. But what do these stored signals actually do? In essence, each waveform acts as a measurement for different components of the video signal. Video components such as sharpness and smear (Frequency Response Signal), brightness (Black Level Signal), contrast (White Level Signal), shadow detail (Luminance Signal), hue (Chroma Phase Signal), snow and noise (Signal-To-Noise Signal) and plenty of other elements of the transfer can all be monitored. In addition, at the end of the program material, additional single frame test signals are provided to consumers to test brightness, contrast, hue, color level, geometry and further parameters.

On the audio side, additional proprietary signals allowed for the testing for all aspects of sound performance. Consisting of a series of tones at a variety of frequencies and levels, these signals were recorded on the soundtrack like the video signals. Characteristics of the sound that could be monitored and maintained included frequency range and response, proper balance between dialogue, effects and music, as well as overall loudness.

Once the laser disc master is made, THX then moves to inspect the "stamper." This is the physical device that actually stamps, or presses (just like a CD or DVD) the laserdisc "grooves." Another proprietary computer test process is then applied to the resulting test discs, which again compares the test signals. THX "QC," or quality control, technicians (those guys in funny white lab coats) also examine and must ultimately approve all test discs. If any problems or errors occur, the pressing will be rejected and must be repeated until success results, or the disc will not be certified.

Once the quality of both the audio and video was assured across the entire process, THX engineers then conduct complete diagnostic tests of the technical equipment, and supervise the entire manufacturing process. THX technicians continue to monitor the duplication process, and offer any assistance with mechanical or pressing concerns. The final finished discs are also inspected and tested on a variety of equipment and players, as well as once again being compared with the original test signals. Once all phases of the production are approved, the laserdisc is granted the THX seal of approval, and sent out to retail shelves.

Entering The Digital Realm

By the mid 1990's, THX had successfully created an identifiable and well-regarded brand name. Thousands of theaters and dubbing stages around the world met with THX specifications, and Dolby Digital 5.1 became the de facto sound carrier for the new DVD and High-Definition Television standards. But perhaps most importantly, the THX logo on a Laserdisc or piece of A/V equipment was considered as a source of pride for many a home theater enthusiast, and the consumer electronics press.

But looming on the horizon was a new technological paradigm that threatened to completely change the consumer electronics, motion picture and communications industries: digital. But THX and Industrial Light and Magic, under the Lucasfilm banner, would become one of the few corporations to almost seamlessly transition from the analog to digital realm. The resounding success of the effects in Terminator 2 and Jurassic Park would completely revolutionize the art of filmmaking, largely thanks to the work by ILM and Lucasfilm.

So, in part three, we examine THX's entrance into the digital realm, and take a look at the new THX DVD Digital mastering Program, as well as what role THX may play in the growing home theater market.

Additional Resources: "The THX Laserdisc Program" by S. Ross Hering and Susan Griffin, Widescreen Review, Summer 1993. For further information, visit THX and Dolby Labs online.