Session	Understanding High-Magenta, Cyan-Dye and Red LED Readers - Implications and Strategies for Optical Soundtracks
Panel Coordinator Panelists	Robert Heiber President, Chace Productions Dr. Alan Masson Eastman Kodak Co Douglas Greenfield Dolby Laboratories
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ABSTRACT

The biggest change in optical soundtrack technology since the introduction of the digital optical sound formats in the early 1990s is currently underway. These changes - high-magenta and cyan dye optical soundtracks and red LED (light emitting diode) readers - have a significant impact on asset managers, archives, restoration professionals and repertory exhibition. This presentation will explain how these changes in optical soundtrack technology affect not only the sound elements in storage but also the creation of new soundtracks for the future. The background surrounding this change and the current status of this transition will be discussed. Audio examples will demonstrate problems that may be encountered and the panel will present strategies for dealing with the issues that range from exhibiting legacy material on red LED readers to using tracks manufactured prior to this change for new prints. Guidelines will be distributed to attendees.

PRESENTATION

Introduction

New developments in optical soundtrack technology are ushering in new issues for asset managers, archivists and repertory release distributors. Cyan dye, High-Magenta, and red LED (light emitting diodes) readers are part of the new lexicon of this change in sound technology. Unlike the introduction of the digital optical sound formats in the early nineties, which brought high quality digital sound to theaters, these new developments are designed to reduce laboratory costs and be more environmentally friendly. How this transition will impact the exhibition of legacy motion pictures, especially color prints from the Eastmancolor era (1951–today), is not as well understood.

Originally presented in 2001 at the Portland AMIA conference, Understanding High-Magenta, Cyan Dye, and Red LED Readers continues to examine how this change impacts the manufacturing and exhibition of classic motion pictures.

To better appreciate the complex issues that surround this subject, this paper will first describe the basics of printing optical soundtracks on film and the creation of the cost-saving and environmentally friendly cyan dye program. Next the issues surrounding the exhibition of optical soundtracks, historically and during this transition, are discussed. With a foundation established in printing and playback issues, the critical discussion of the exhibition of legacy materials can commence.

While the research conducted for this paper provided valuable new insights into the issues of the transition to cyan dye technology, it should be emphasized that the results are not scientifically conclusive, due to the small sample of material tested at this time. However, the data corroborates basic assumptions and should provide a base of reference for making practical decisions.

Optical Sound Tracks

First we shall consider how optical sound tracks are put onto film release prints, and the photographic issues that have led to the need to change from silver to cyan dye sound tracks. The sound track is derived from a magnetic recording that is edited, mixed and transferred onto sound negative film using a special camera. The processed sound negative and the picture negative are printed together in synchronization onto the composite release print. (Figure # 1)

In a black and white print, both the picture and sound track are formed of silver images. There have been many formats of optical sound tracks over the years. Here are examples of variable area and variable density tracks. (Figure # 2) Both have the ability to modulate the brightness of a beam of light in the sound reader of a projector.

Reproduction of sound from the black and white (silver) sound track used an exciter lamp plus a photoelectric cell to pick up the fluctuations in light passing through the sound track, as modulated by either the width of clear area of the track or its density, depending on the track format. In the early days, the photocells were mostly sensitive to infrared light, which is well modulated by the silver sound track image due to its optical density to infrared light.

Redevelopment of Silver Sound Tracks

With the introduction of the Eastmancolor system in the early 1950s, it was found that the dye images of the color print film would not modulate the infrared light picked up by the projector photocell. It was necessary to provide a silver sound track along with the color dye picture images. This was achieved by re-developing the silver image of only the sound track portion of the film. This is a complicated procedure with a number of potential problems, so laboratories have been looking for ways to eliminate sound track redevelopment, almost from the date of its introduction.

Redeveloping a silver sound track on color print film requires several extra stages. (Figure # 3) These stages are a first fixer and wash, and a sound-track redeveloper and wash. The redeveloper is a very active black and white developer made viscous with a thickening agent. It is precisely applied with a narrow applicator wheel to the sound track area only. After redevelopment, the redeveloper is removed by a spray rinse. Redevelopment is a tricky operation, especially in today’s high-speed processing machines, and errors can occur that result in rejected prints and additional waste. Also, the redeveloper is quite hazardous to technicians and a lot of chemicals and water are used.

Environmental Issues

In addition to the rejected prints and the hazardous chemicals’ negative impact on technicians, there are two environmental issues. First, a large amount of chemicals and water end up going down the drain and adding to the lab’s effluent load. Second, the silver track in the print becomes an environmental issue when prints are destroyed after their use in theatres. Silver is a heavy metal as well as being a valuable resource.

It is estimated that film labs annually make over ten billion feet of color release prints worldwide. This continues to increase with the use of “Day and Date” simultaneous worldwide releases of over 10,000 prints for major movies. Figure #4 estimates the quantities of chemicals and water used to redevelop the silver sound tracks. You can imagine the environmental benefits of eliminating the use of these chemicals and water in silver sound track redevelopment.

The Cyan Solution

The “Cyan Solution” is to replace the redeveloped silver sound track with a track using the cyan dye already existing in color print film, which does not require redevelopment. A problem is that existing white-light sound readers in projectors do not “see” a cyan dye sound track very well. Therefore, it is necessary to change to sound readers that use red light from a bright LED, like the ones now used in automobile taillights and red traffic lights, along with a red-sensitive photocell. Why was the cyan dye chosen?

We can demonstrate why a combination of cyan dye track and a red LED reader was chosen for silver-less dye tracks by placing a strip of cyan filter over strips of red, green and blue filters on a light box. (Figure #5) Red light is absorbed by the cyan filter (it goes black), while the green and blue lights are unaffected. Variations in the amount of cyan dye, as in a variable-area sound track, will modulate the amount of red light transmitted by the track and received by the photocell.

The overall plan is to replace the silver track with a cyan dye track and replace the white-light readers with red light readers. Unfortunately, this is not as simple as it sounds. The change cannot be made instantaneously, due to the amount of time necessary to change all the projectors worldwide. Also, a “chicken and egg” situation exists: theatres are waiting for cyan releases before spending money to install red readers, yet distributors want to be sure that most theatres have installed red readers before releasing their movies with cyan dye tracks.

Due to some incompatibilities between the old and new readers, it was necessary to have a transition period of several years, during which a compatible track format called “High-Magenta” was used. The High-Magenta track can be reproduced using either type of reader. This avoided the need for a dual inventory of silver and cyan dye track prints, which would be a nightmare for labs to produce and even more so for distributors. A single inventory of compatible prints was essential. The conversion is therefore a two-step process from today’s silver tracks, via High-Magenta tracks, to the ultimate goal of cyan dye-only tracks, as shown in Figure #6.

Silver tracks are redeveloped to contain silver plus cyan and magenta dye images (although the dyes are not actually used). They are reproduced using a white light reader. They can be reproduced with a red reader, but there can be a little distortion, as has been reported from some theaters that have already installed red readers.

High-Magenta tracks, used for an interim period of a few years only, are also redeveloped and contain both silver and magenta dye. High-Magenta tracks give excellent quality when reproduced with white light and red readers.

Cyan dye tracks do not require redevelopment but can only be reproduced satisfactorily using a red reader.

Thus the issues with optical sound tracks are:

1. The silver sound track on B&W film is reproduced with a white light reader.
2. Color film requires redevelopment of a silver track for reproduction with a white light reader.
3. Redevelopment causes quality and environmental issues for the labs.
4. The cyan dye format allows elimination of silver redevelopment.
5. An intermediate format called High-Magenta was necessary for compatibility with both white and red readers during the transition period while projectors were being fitted with red readers.
   

Before discussing the transition to cyan dye sound tracks, it is necessary to have a background in the reproduction of optical sound and the impact this new technology has on the exhibition of motion pictures.

The Quality of Sound Tracks

Optical sound reproduction is not new, and the engineering issues have been well understood (and quantified) for many years. As engineers, we are concerned with:

• Distortion: the presence of unwanted components along with desired program.

• Signal to noise ratio, which describes the difference between reference levels of program modulation compared to the inherent noise of the film base and emulsion in its clear area.

• Frequency response, which describes the audible range of sound, from low bass to high treble, with minimum deviation in level across this desired range.

These three characteristics (distortion, signal to noise ratio and frequency response) define the fidelity of soundtrack reproduction.

For stereo soundtracks, we are concerned with:

• Channel balance, which is influenced by both illumination uniformity and azimuth adjustment.

• Inter-channel crosstalk, which is influenced by the design and the implementation of the optical path in the sound head.

Forward Scan Readers

Until 1995, most analog sound heads were direct or forward scan types with white light (tungsten filament) illumination. (Figure #7)

The principles of direct scan sound heads consist of condensing lenses within the lens tube that focus an image of the filament onto a mask with a narrow slit. An objective lens within the tube focuses an image of the illuminated slit on the film plane. Typically, there is an image reduction of about 2:1,providing an image of the slit that is about .080 inches wide and 0.6 mils high. The solar cell is placed behind the film plane, but as close to the film as possible. (Figure #8)

Even so, the image diverges slightly by the time it hits the solar cell. Fine adjustments are difficult due the image reduction in the optics. For stereo solar cells, because the image diverges past the film plane, a portion of the light intended for the right track impinges on the left channel of the solar cell, and vice versa, so there is always some unintended inter-channel crosstalk. Also, the illumination falls off toward the outside edges of the soundtrack, producing some harmonic distortion.

Reverse Scan Readers

Reverse-scan optics have a number of advantages compared to direct scan optics. Indeed, reverse scan optics were used exclusively for the optical recording systems used in dubbing studios before the introduction of 35mm magnetic recorders in the late 1940s. (Figure #9)

The soundtrack is illuminated from behind by a very even, very bright light source. In early sound heads, the source was a tungsten filament, with condensing lenses focusing an image of the filament just past the film plane, providing a diffuse field at the film plane. Modern readers use high intensity LEDs that do not require additional optics.

An objective lens focuses an image of the soundtrack onto a slit mask just in front of the solar cell. Typically, the image is magnified by about three times, so the actual slit height may be 1.8 mils to achieve the same scanning performance at a 0.6 mil slit in a forward scan reader, allowing more light to reach the solar cell. (Figure #10)

The solar cell is proportionately much closer to the slit for reverse scan compared to direct scan. Two advantages accrue: the light intensity across the slit is kept constant, reducing harmonic distortion, and because the image divergence past the slit is negligible, there is virtually no crosstalk from channel to channel, resulting in very stable stereo performance. Also, LED light sources last much longer than tungsten filament incandescent lamps.

In 2001, we estimated that out of about 120,000 screens worldwide, 65,000 had been fitted with red LED readers—a bit more than half. In North America the percentage was better, with 19,000 screens out of a total 35,000 fitted with red LED readers. Virtually all theaters built since 1997 have red LED readers.

These numbers have gone up substantially since 2001, but we no longer track them for a couple of reasons. We derived the estimates from the sales figures for both the red LEDs and the OEM reverse-scan reader kits shipped to projector manufacturers. We are now well into the replacement cycle for red LEDs, so we can’t separate red LEDs intended for new installations from those purchased for maintenance or replacement.

More importantly, the time for cyan dye tracks is at hand. The environmental and economic advantages of cyan dye tracks have achieved the critical mass necessary to move studios to cyan-only releases. Theaters with traditional white light readers will find the time has come to retrofit—at what is really a nominal cost.

Conversion to Dye Tracks

The (long) path to cyan dye-only sound tracks started as long ago as January 1998, when Warner Bros. released 100 High-Magenta prints of City of Angels, printed at Technicolor. No problems were anticipated, as this format was designed to be compatible with both white-light and red sound readers, and in fact no problems were reported. A year later, You’ve Got Mail was released with 100% High-Magenta tracks, also by Warner Bros. and printed at Technicolor. Since then this format has been widely adopted. At the same time, new theatres were being built with red readers supplied as standard and the Dye Track Committee was working hard to publicize this change and encourage existing theatres to retrofit red readers to their projectors. The goal was 85% conversion to red readers before it would be practicable to make the second change, to cyan dye sound tracks.

Reprinting Legacy Negatives

While major studios are expected to make new sound negatives from their magnetic masters for printing High-Magenta or cyan dye tracks, the issue we are discussing in this paper is the direct reprinting of legacy sound negatives by other movie owners who cannot afford the cost of making new sound negatives. We need to define what we mean by “legacy.” For our purposes, a legacy sound negative is one that was prepared for color printing prior to January 1998. That was the beginning of the use of High-Magenta tracks on release prints. Legacy negatives were intended for printing to give silver sound tracks.

Cyan Dye Test Releases

As with High-Magenta releases, the first test releases of prints with cyan dye tracks were limited and had the additional requirement of going to theatres playing the analog sound track, not digital, and using red readers. The first two limited cyan releases were Get Over It and Jay and Silent Bob Strike Back by Miramax in 2001. Again, no problems were reported by the theatres, which were provided with an 800-telephone number to call if necessary.

Since then, theatres have been encouraged to urgently install red readers in preparation for 100% cyan releases, knowing that if they tried to play a cyan track on a white-light reader they would encounter a large (11-12 dB) drop in sound level and probably decoding errors with Dolby SR analog sound tracks. To help theatres understand the problem, Dolby Labs produced a short track-only demonstration film in the US, as did Technicolor in London.

The Role of Industry Organizations

The Dye Track Committee mentioned earlier has been the driving force in the conversion, first to High-Magenta and now to cyan dye sound tracks. Ioan Allen of Dolby is the convener and Alan Masson of Eastman Kodak Company is the secretary. The website (www.dyetracks.org) contains comprehensive technical information and includes the latest press releases from distributors. The Kodak website (www.kodak.com/go/motion) also has a lot of useful information. The Dye Track Committee has been working with other industry organizations, including MPTAC (Motion Picture Theatre Associations of Canada), which recommended its members be 100% converted to red readers by January 1, 2003 and NATO (National Association of Theater Owners), which made a similar recommendation to its US members to be converted by July 2003. It is hard to obtain exact figures, but it is believed that a very high percentage of theatres in the US, Canada and many other countries are now converted, justifying the long awaited introduction of cyan tracks.

100% Cyan Dye Feature Releases

The good news is that the very first 100% cyan dye track release happened on September 19, 2003. This was Anything Else starring Woody Allen from DreamWorks SKG. All prints for North America had cyan dye tracks.

Then at Showest 2004, MGM announced that all their US releases would employ cyan tracks starting with Soul Plane on May 28, 2004, and at the same show Disney announced that their first 100% cyan release would be Mr 3000 in September 2004, followed by all Disney releases worldwide beginning on January 1, 2005.

High-Magenta Transition May be Longer for Re-Releases

Originally the idea was that the High-Magenta format would be used only during the few years of the transition from silver to cyan tracks for first-run features. It is expected or hoped that the cyan transition may be completed by the major release printing labs for features in 2005 for well-known environmental reasons. However, the transition period may be much longer for restored films playing in repertory theatres, which are likely to be slower installing red readers. It is therefore suggested that High-Magenta is a practical track format of choice for the restoration of legacy movies. This means that boutique labs in this field will need to retain their capability to redevelop silver tracks for an indefinite period of time.

Technical Issues with High-Magenta Printing

The High-Magenta track format looks like the practical solution to the issues of printing and reproducing legacy sound tracks. The question is if an existing legacy sound negative can be used to make a good High-Magenta track on color prints.

The High-Magenta track requires a somewhat higher negative density than the silver track. For KODAK Panchromatic Sound Recording Film 2374, the density is in the range of 2.3 - 4.0 for High-Magenta, compared with 2.0 - 3.5 for silver. For EASTMAN EXR Sound Recording Film 2378 (orthochromatic), a High-Magenta track requires a density in the range of 2.1 - 3.2 compared with 1.7 - 3.1 for a silver track.

Thus a legacy negative made for printing a silver track may require some adjustment of the High-Magenta print density to provide cross-modulation cancellation. For “recent” legacy negatives made on currently-available film stocks, this is likely to mean that a lower print density will be required to provide cross-modulation cancellation, but this is not a general rule.

When this issue was first considered, there was hope that it would be possible to formulate a simple rule-of-thumb for the print density adjustment. However, the many different sound negative stocks supplied by the manufacturers over the years (assuming they could be identified) and the different print stocks all had different image spreads, requiring different print densities for cross-modulation cancellation. Thus no simple rule-of-thumb has been found for print density adjustment, at least for now.

Optical Soundtrack Quality Metric

The quality of an optical soundtrack depends critically on the optimum exposure of both the soundtrack negative and the positive print. An elegant and ingenious method of determining the correct exposures is called cross-modulation analysis. Optimum exposures result in a condition we refer to as cross-modulation cancellation, which provides the least possible distortion for the soundtrack. For the listener, a very sensitive subjective assessment is whether or not there is unpleasant distortion, or “splash”, on sibilants of speech. A trained listener will be able to detect variations of as little as 5 points in density on positive prints in direct comparison to the master recording.

These considerations may represent a Quality Formula, wherein optimum cross-modulation cancellation equals minimum audible sibilant distortion.

Testing for the Optimum Print Density

Ideally, a cross-modulation test needs to be done with a family of print densities to find the one with minimum distortion. Unfortunately, legacy negatives typically do not contain a cross-modulation test signal, so we have to resort to a listening test to determine the cancellation density.

Listening tests are quite easy. All you need are a good pair of ears and some suitable program material with dialog containing a lot of “sibilant” sounds. “Sibilant” comes from a Latin word meaning “hissing” and refers to sounds such as the letters “s” and “z”. A listening test involves making a density series or “family” of prints from a legacy negative, with densities above and below those normally used by the lab, and carefully listening for distortion of the sibilant sounds when they are reproduced. The print with the minimum sibilant distortion provides the aim density for printing the job.

We need to consider the effect on other sound quality metrics when we adjust the print density to cancel the negative distortion. Recall the other metrics are signal to noise ratio (SNR) and high frequency response (HF). Predictably, the signal to noise ratio increases (better) as the track density increases relative to the minimum density (D-min) of the film. But at the same time the image spread also increases, filling in the fine detail of the high frequency sound images on the film and degrading the HF response. Normally the choice of print density is a compromise between SNR and HF response. If we move too far from that density then one of these other quality metrics will suffer. However, hearing cross-modulation distortion, which is quite annoying to the ear, is generally easier than hearing a small increase in noise or loss of the highest frequencies. The optimum print density range for the highest quality is quite narrow: 0.8-1.1 infrared density for a High-Magenta track on KODAK Vision Color Print Film 2383 or KODAK Vision Premier Color Print Film 2393.

Bye Bye Birdie Test Case

While the listening tests described above will often give a satisfactory result, sometimes these tests are inconclusive. Bye Bye Birdie, originally released in 1963, was re-mastered from a 3-track stereo mag for a new stereo optical soundtrack negative in 1996. When the 1996 legacy negative was used to make a new print in 2000, the resulting print was not satisfactory. This experience formed the basis for research into making High-Magenta optical tracks from legacy negatives.

For Bye Bye Birdie we had two pieces of critical information about the soundtrack negative. The optical negative stock was Agfa ST8D and the visual density of the negative was 270. Armed with this information, an 11-step single density cross-modulation test was made to duplicate the positive density aims of the subjective wedge test. The advantage, of course, is that we can now analyze the distortion performance.

The results are plotted in this graph (Figure #11) for both white and red light illumination. The plot illustrates that the range we chose for our first test was too high to include the cross-modulation cancellation point. Extrapolating from these curves, the result is shown in the next graph. (Figure #12) The white light curve overlays the red light curve, for a single extrapolated cancellation point at an IR density of 0.98.

To confirm the validity of the extrapolation, a 20-step cross-modulation series was made over the range of visual densities from 200 to 360, again on Agfa ST8D. We made two High-Magenta positive prints on Kodak 2393 stock at the minimum (.80) and maximum (1.10) IR positive aim densities recommended by Kodak for 2393.

The results for white light are plotted in this graph. (Figure #13) It is evident that the cross-modulation cancellation point for a negative density of 270 falls neatly between the two density aim curves. Interpolating between the two boundary curves, the optimum aim density is about 1.0.

The results for red light are plotted in this graph. (Figure #14) Again, the cross-modulation cancellation point falls between the two density aim curves, although the range of cross-modulation distortion values is higher. Interpolating between the two curves, again the optimum aim density for the original negative is about 1.0, very close to the extrapolated value of 0.98 found in the plot of distortion versus aim density.

It should be noted that density is not an absolute indicator of image spread, which is the critical factor for optimum exposure and expressed either as a percentage distortion or in decibels as the cross-modulation product. Also, the characteristics of different batches of the same negative stock vary somewhat. In this instance, the results demonstrate that a new print of Bye Bye Birdie at a positive aim density of 1.0 would have satisfactory results.

Summary

The adoption of cyan dye soundtracks as the primary method for exhibition is upon us. By 2005 cyan dye will likely be the predominant soundtrack format in North America and selected European countries. However, in the world of repertory release of legacy motion pictures, the conversion process to cyan dye tracks is likely to be extended or may not happen at all. For this reason, the High-Magenta soundtrack, which is compatible with both white light and red LED sound playback systems, appears to be the best practical solution. To accommodate this new format, new guidelines will have to be adopted in several areas.

From an inventory perspective, arrangements will have to be made for the identification of new negatives, which are optimized for either High-Magenta or cyan dye printing. It is important to remember that the negative density of the High-Magenta soundtrack is also compatible for producing cyan dye soundtrack prints. Additionally, the test data on Bye Bye Birdie corroborates the claim of satisfactory playback of High-Magenta soundtracks by both white light and red LED readers, since the cross-modulation cancellation tests yielded nearly identical results when read with white and red light.

To summarize our guidelines for printing legacy negatives, a legacy sound negative density is not optimized for printing both a silver print and a High-Magenta (or cyan dye) print. A lab’s normal print density for High-Magenta prints may not provide cross-modulation cancellation for legacy negatives because a High-Magenta print requires a negative with a higher density than for a silver print. The use of a legacy negative therefore requires the High-Magenta print density to be determined by test. Ideally this is a cross-modulation test, but legacy negatives do not usually include a cross-modulation test signal. Thus it will be necessary to do a listening test.

Existing black and white prints were made to provide cross-modulation cancellation when reproduced using white-light readers. However, tests with B&W prints from the archives have shown that most of them also play very well with red readers. When making a new B&W print with a legacy negative, a listening test can ensure an optimum print.

The type of track (silver, high-magenta, and cyan) and the type of reader (white light or red LED) both affect playback in the theater. A silver track will always have slightly higher measured distortion when played back with visible red light, compared to tungsten. In practice, this may or may not be discerned by the moviegoer. The subjective effect, if evident, will be an increase in sibilant distortion. High-Magenta soundtracks will play equally well with either visible red or white light readers, because the cross-modulation cancellation point is the same for either source, by design. A cyan track must be played with a visible red source, by design. A cyan track played with a white light source will be unacceptably noisy.

The authors would like to acknowledge and thank the contributions of the laboratories, studios and individuals who made this report possible:

• Cinetech, Cineric, Inc., Deluxe, Image Laboratory, NT Audio, THX®
• 20th Century Fox, Sony Pictures, Warner Bros.
• Tim Andrews, Corey Bailey, April Connelly, Mark R. Curry, Jess Daily, Robert Easton, Brian Geer, Jeff Gersh, Dale Gervais, Todd Iverson, Shawn Jones, Simon Lund, Bobby Mapula, Joe Olivier, Thom Piper, James B. Young

SPEAKER BIO

Bob Heiber

Bob has been involved in film sound preservation since 1990 when he joined Chace Productions. A member of AMIA since 1991, SMPTE, the Academy of Motion Pictures Arts and Sciences and ACVL, Bob has served on the National Film Preservation Board Advisory Task Force and the Library of Congress panel for the State of American Television and Video Preservation. He has spoken on film sound preservation, restoration and re-mastering at AMIA, ACVL, SMPTE and ARSC conferences. Prior to joining Chace, Bob was the Manager of Technical Operations at Warner Hollywood Studios and an award winning documentary/industrial filmmaker in Chicago, Illinois. Bob graduated from Purdue University in 1973 with a Bachelor of Arts in Radio-TV-Film.