Red Readers, Silver, High-Magenta, and Cyan Analog Soundtracks: Reprinted with permission of SMPTE This paper reviews the benefits of silverless, cyan dye tracks to the motion picture industry, the status of red reader deployment in motion picture theaters, the effect of red reader characteristics on the sonic performance of silver and dye tracks, and the need for the intermediate step of first moving the industry to "high-magenta" color balance reapplicated soundtracks before changing over to silverless cyan dye tracks. In addition, an updated high-magenta and cyan dye track industry road map is presented. At the 138th SMPTE Technical Conference and World Media Expo held in Los Angeles in October 1996, a paper entitled "Red LED Reproduction of Cyan Stereo Variable Area Dye Tracks," by Paul R. Goldberg (Zoran Corp.), Ioan Allen (Dolby Laboratories), Frank J. Ricotta (Technicolor), and Richard C. Sehlin (Eastman Kodak Co.), was presented. The paper discussed the means by which the motion picture industry could finally eliminate its dependence on analog sound track redevelopment, an additional processing step that reintroduces silver into analog soundtracks printed on color stock. A soundtrack reading mechanism, based on the use of a red light-emitting diode (LED) illumination source, was described. The mechanism allows the reading of a cyan dye track with fidelity essentially equal to that presently obtained from a standard "silver track" reproduced by a conventional soundtrack reader. The paper also presented the results of in-depth studies conclusively demonstrating that red LED readers reproduce silver tracks and cyan dye tracks with equal amplitude. This is in contrast to conventional tungsten illumination source readers, which reproduce cyan dye soundtracks with an amplitude loss of ~11 dB. This characteristic of the red LED reader permits the installation of these reading mechanisms in theatres before any change to cyan dye analog soundtrack technology is implemented, and thus allows for an orderly changeover from silver to silverless soundtracks. Industry Benefits of Silverless Cyan Dye Tracks There are numerous reasons why the motion picture industry has been searching for ways to eliminate the need to redevelop analog soundtracks. Some of these reasons are as follows:
Since March 1995, Eastman Kodak Co., Technicolor, and Dolby Laboratories have been working together to perfect a methodology, from a film, laboratory practice, and theatre presentation equipment standpoint, that will allow the industry to fulfill the objective of eliminating the need to redevelop release prints. As of April 1996, Agfa, CFI, Deluxe, and Fuji, have been part of the team. The result of this effort is the creation of an analog soundtrack reader technology based on a red LED illumination source, and the definition of orderly changes to current laboratory practice, which will ultimately result in the industry changeover to silverless cyan dye tracks. In June 1996, Zoran Corp., an impartial industry observer heavily involved with state-of-the-art industry initiatives such as digital versatile disc (DVD) and digital nonlinear film editing, joined the activity. Red LED Reader Deployment1 At the present time red LED analog reader technology is being actively sold throughout the world by almost all projector equipment manufacturers. Since red readers were introduced in May 1996, over 8,000 red LED readers have been installed, as shown in Figure 1. It is estimated that by December 1998 there will be over 15,000 red LED readers operating on a daily basis in theaters worldwide. These shipments include readers built into newly produced projectors, as well as upgrade kits for projectors already in the field. Currently all new Cinemeccanica, Christie, and Kinoton projectors are being shipped with red readers. By July 1997 all new Strong projectors were also based on red LED technology. From a projector upgrade standpoint, Kelmar is presently shipping red LED reader kits for Ballantyne, Bauer, Century, Cinemeccanica, Denko, RCA, Simplex, and Tokewa projectors. Red LED reader kits from Component Engineering for Century and Simplex projectors have been available since the summer of 1997. The response to the use of red LED readers has been overwhelming. The reasons for this are:
Silver and Cyan Dye Track Performance when Reproduced by Red Readers2 With so many red LED-based analog readers already in service, and thousands more being installed in new theatres and retrofitted into older theatres every month, it is important to understand the effect of red readers on the sonic performance of analog soundtracks. Amplitude Performance Unlike silver tracks, which exhibit wideband absorption over an extended range of wavelengths, cyan dye tracks exhibit peak absorption at a wavelength of ~660 nm for all major brands of release stock. Red LED reader illumination wavelength is 660 ± 20 nm. Since silver tracks absorb well into the visible portion of the light spectrum, a reader that employs a 660-nm red LED light source will be able to reproduce silver tracks and cyan dye tracks with almost equal amplitude; conventional tungsten readers will not. This is depicted in Figure 2. The "C" preceding the film stock numbers, along the horizontal axis of the graph, indicates a cyan dye track print. As you can see, the tungsten reader reproduces a cyan dye track print with a loss of ~11 dB, whereas the red LED reader reproduces cyan track and silver track prints with almost equal amplitude. This is why silver and dye tracks can be interchangeably played on red readers with no gain adjustment of the playback electronics. Crossmod Performance A conventional silver print, played back on a red LED reader, will not display the same crossmod cancellation characteristics as it would if it were reproduced on a standard tungsten reader. Figure 3 shows that a silver track read on a tungsten reader will display good crossmod cancellation when the negative employed to print the track has a density of 2.18 optical density units (O.D.). The same track needs to be printed from a negative with a 2.6-O.D. density if it is to display good crossmod cancellation when reproduced on a red LED reader. The filter pack used to create the high-magenta silver print in Figure 3 is W12 + 0.2 ND + 0.90 C. Fortunately, there is a sound negative density, in conjunction with a print color balance, that will produce a release print capable of playing equally well, in terms of crossmod cancellation on both tungsten and red LED readers. This print is called a "high-magenta" applicated print and requires a negative density of ~2.7 O.D. with a print color balance of 1.09 IR, 1.44 Y, 2.02 C, 3.82 M. Figure 4 shows the crossmod results from such a print. The same negative used to print a high-magenta silver track release print can be used to print a cyan dye track release print. Figure 5 shows the crossmod results from a cyan dye track print reproduced with a red LED reader. The target color balance for this print was 0.36 IR, 0.36 Y, 2.14 C, 0.38 M. The graph shows that the best crossmod performance was achieved with a negative density in the range of 2.6 O.D. Table 1 summarizes the print color balances for a standard silver soundtrack, a redeveloped high-magenta soundtrack, and a cyan dye soundtrack.
Noise Performance Tests have demonstrated that readers based on broad band tungsten, or white light, illumination sources are quieter than readers based on narrow band red LED illumination sources (660 ± 20 nm light energy spectrum). It is believed that this is due to the fact that when the track is illuminated by broad spectrum white light, the incoherent noise sources from each of the film's color layers add on a random basis and thus the noise "averages out." If a narrow spectral band illumination system is employed, this averaging cannot take place and thus the signal-to-noise ratio is impaired. This is true whether a standard silver track, high-magenta applicated track, or cyan dye track is being presented. It is also independent of the type of release stock employed. Figure 6 depicts this phenomenon for a standard silver track on Agfa release stock. Note that in all cases the curves for the red reader "look worse than they actually sound." This is because it is extremely rare for the bias line to fully open during actual movie sound track presentation. Extensive listening tests at Dolby Laboratories have shown that the use of Dolby SR encoded soundtracks, although not completely eliminating the additional red reader noise, reduces its effect to the point that air conditioner noise will significantly mask the problem. The Need to Change to High-Magenta Before Cyan From the previous discussion it can be seen that the industry switch to high-magenta applicated soundtracks is required for two very important reasons: first, the need to mitigate any diminished crossmod performance associated with the rapidly expanding use of red readers and, second, the need to facilitate the industry change-over to cyan dye tracks. Although a quality of audio reproduction, which the average movie patron would not detect as being different from the current standard, and, may in fact, because of increased stereo separation, wider frequency response at high power levels and significant reduction of illumination nonuniformity distortion perceive as being an audible improvement, is produced by red readers, a closer match, with regard to crossmod performance, can and should be achieved. Note that the use of high-magenta soundtracks achieves this goal, along with the additional very important benefit of easing the industry transition to cyan dye tracks. Since the same higher density negative is used for both high-magenta and cyan dye prints, the changeover to high-magenta soundtracks would also initiate the industry's use of the higher density sound negative required for cyan dye tracks. Thus a major cause of potential error and cost would be eliminated if high-magenta tracks became the industry standard before cyan dye tracks are actually used on major motion picture releases. High-Magenta and Cyan Dye Track Industry Road Map A five-part road map for the industry changeover to cyan dye tracks was presented at SMPTE'S First Annual Spring Film Conference and Exhibit, in March 1997.3 This road map, updated to reflect progress that has been made since then, calls for the following. 1. Changing over to high-magenta reapplicated analog soundtracks as quickly as possible. Thus far, much work has been done in this regard. To date, CFI, Deluxe, DuArt, Fotokem, and Technicolor have performed tests that verify there is essentially no difference in the audio quality derived from prints made with high-magenta soundtracks, as compared with prints made with conventional redeveloped silver tracks, whether they are played on tungsten or red readers. Work is currently going on in the area of high speed reproduction of high-magenta release prints. There is also a need to provide studios with the confidence that the change to high-magenta tracks will be essentially transparent. To this end, the road map calls for working with the sound houses associated with major motion picture studios on controlled tests that are designed to demonstrate sonic differences between a normal silver track print, produced with a standard density negative, and a high-magenta silver track print made from a higher density negative. When these high-magenta tests are satisfactory to all concerned, the head of distribution for the studio, associated with a particular sound transfer house, can be contacted. At this point, the title and date for a high-magenta pilot test can then be set. 2. Promoting the cyan dye track concept to all segments of the industry. In an effort to introduce the dye track concept to the exhibition segment of the industry, two articles on cyan dye tracks have already appeared in Eastman Kodak's quarterly publication "Film Notes For Reel People." More in-depth articles are planned. Also, Ioan Allen of Dolby Laboratories presented the cyan dye track status at the "Intersociety" meeting that took place on March 6, 1997, at ShoWest in Las Vegas. To provide individuals associated with the Hollywood sound transfer facilities with needed high-magenta and cyan dye track information, presentations at a meeting of the SMPTE Study Group on Audio Production and Post-Production for Motion Picture and Television Entertainment Programming (A 12.68) are planned. Broad-ranging motion picture industry promotional activities should begin immediately after the high-magenta pilot tests are complete and successful. 3. Initiating cyan dye track pilot tests when sufficient numbers of red LED readers have been installed in theaters, and cyan dye track promotional efforts have notified the industry that the change to cyan dye tracks is on the way. Although it is estimated that ~8,000 theatres worldwide are equipped with red LED readers as of December 1997, it must be noted that most of them are installed in new theatre complexes. To feel comfortable that there is no need for dual inventory of both high-magenta release prints and cyan dye release prints, sufficient red LED readers need to be installed in previously built theaters as well. Given the current rate of red reader installations shown in Fig. 1, it is estimated that ~15,000 theaters worldwide will be equipped with readers by December 1998. This number is sufficient to release small numbers of cyan prints associated with a major motion picture, to theaters known to be equipped with red LED readers, thus signaling the beginning of the industry's changeover to cyan dye tracks. 4. Releasing a limited number of movies in 100 percent "cyan." It is estimated that sufficient red LED readers will be installed worldwide by December 1999 to allow the release of a major motion picture in 100 percent cyan. By widely promoting this release six to nine months before it occurs, projector manufacturers, exhibitors, film labs, and studios can be prepared to support this important change in industry practice. 5. Completely changing over to 100 percent cyan dye tracks. Conclusion Cyan dye tracks are on the way. The rapid acceptance and deployment of red LED reader technology throughout the exhibition segment of the motion picture industry is making it possible. The industry now has an unprecedented opportunity to finally eliminate the need to redevelop analog soundtracks and gain all the benefits that can be derived by the use of a silverless analog soundtrack process. Reference and Endnotes 1. Data on red reader installations from Dolby Laboratories. 2. All data presented in this section was derived from tests performed by Dolby Laboratories, Eastman Kodak Co., and Technicolor between March 1995 and June 1996. 3. Paul R. Goldberg, "High Magenta and Cyan Analog Soundtracks: A Progress Report," presented at the First Annual SMPTE Spring Film Conference. Los Angeles, Calif., March 22, 199T
Paul Goldberg is vice president of systems solutions and audio products for Zoran Corp., a leading supplier of integrated circuits and software for digital audio and video applications. Before joining Zoran, he was the leader of film products development at Dolby Laboratories. In this capacity he directed the research, development, and commercialization of the Dolby Digital sound on film system and developed the use of red LEDs for the purpose of reading analog and digital soundtracks. Goldberg received a B.S. degree in electrical engineering from the University of Minnesota. He holds 16 patents in film sound, optical data storage, video image printing, medical ultrasonic imaging, and medical diagnostics. He is an active member of SMPTE, AES, SID, and the IEEE. |
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