Dolby Cat 566 Illumination Uniformity test film and how to use it...

[Tony Bandiera Jr]

I'm on a roll today, so... and in light of our recent losses of some wonderful people filled with knowledge of how to work on film equipment, I feel we all need to step up and start threads giving out this kind of information before it is really lost forever.


Next up is the Dolby Cat 566 Illumination Uniformity test film. This film is for use with ALL optical setups, solar cell (Incandescent, LED or IR) Readers, IR or LED, etc. IIRC it even works for MONO solar cells.

The principle is simple. There are six tones of different frequencies positioned across the width across the track, three on one channel and three on the other. They are all recorded to within about 1db or less of each other.

Using the film is easy, you do however need a good RTA capable of 1db per step on the display to see the results. (On the Audio Control SA 3050 I just sold, it was super easy to see because the LED dot display was aligned with the six frequencies used.)

• Run Dolby Tone (CAT 69T) and Pink Noise (CAT69P) to set frequency response AND Dolby level before using this film. Also be sure to run the CAT 97 Crosstalk test as per my other thread.
• Connect your RTA to the optical test points of the processor, combining BOTH channels into a single input to the RTA. Set the resolution to 1db per division/dot.
• Thread the loop making sure orientation and direction is correct.
• Start the projector and allow the soundhead to stabilize.
• Set the RTA input sensitivity to read mid display/scale)
• All six peaks should be equal showing a straight horizontal line. If any are lower or higher, adjust the lateral and/or azimuth (if using a slit lens standard Solar cell setup) to get all six peaks as close as possible to equal.
• Lateral errors will show one side higher than the other. Azimuth error will show one end higher than the other, with a slope. Excessive falloff on both sides will show a droop at each end (frowning). Bad LED segments or dirt (or sagging filament on incandescent) will show one or more of the center four peaks low. Adjust or replace parts as needed.
• If any adjustments were required, re test and set Dolby Tone as per step one.

Like the CAT 97 crosstalk, this film is invaluable to ensure the maximum performance of the optical tracks and ensure that Dolby NR tracks correctly. If your analog sound has spitting, excessive hiss, distortion (especially in the surrounds on loud sounds), excessive spillover in the surrounds, etc. this test along with the crosstalk test will fix most of those issues easily.

[Steve Guttag]

I'll counter that CAT97, in the reverse scan era is of no use. There is nothing it does that other films can't do better. The only "measured" film is Buzz track. As such, that should set the film's lateral placement relative to the cell. CAT566 sets the films lateral placement to the LED as well as indicates if magnification is excessive (both high (right most) and low (left most) tones drop.

Without CAT566, CAT97 can be a poor-man's illumination film as it is supposed to be 100% modulation so if the waveform is clipped on either channel, your LED isn't centered or magnification is excessive if both ar clipped. In X-Y mode if the cross isn't perfect, it indicates uneven illumination too.

Naturally, for forward scan, then yes, CAT97 is needed to minimize crosstalk.

[Ryan Gallagher]

And since this is meant to be instructional, if the term "forward scan" and "reverse scan" are not understood clearly, here is a good little primer from Dolby.

https://www.film-tech.com/warehouse/...LBYSCANREV.pdf

Forward scan being the older method, more likely excited by a lamp and not an LED, incompatible with cyan dye soundtracks.
Reverse scan is the "newer" (late 90s early 2000s) cyan dye track compatible, LED driven, optically improved scanning method.

That said I think plenty of forward scans were converted to LED too? But without all the other benefits of reverse scan.

[Steve Guttag]

Forward and Reverse scan are independent of light sources. There are plenty of examples that disprove to the contrary. Philips on their FP56 and AA2, for example used reverse scan with an excider lamp as did Century with their R4 soundhead (it wasn't great but it was reverse scan with an exciter lamp...long before LEDs). The JAXLIGHT was a common forward scan LED light source, compatible with cyan dye tracks. There were even laser lights used too.

The chief difference is what is focused onto the cell. Was it the slit of light or was it the tracks themselves (with a slit used as a mask)? Even the direction of the scanning wasn't universal. As in, while some would think that forward scan has to do with the reader (Cell) being forward of the film (to the right)...Philips, again, put the exciter lamp on the right and the cell to the left of the film yet that would still be considered "Forward Scan" as it is projecting a slit of light onto the cell with all of the same alignments and characteristics of any other forward scan system.

[Ryan Gallagher]

Forward and Reverse scan are independent of light sources. There are plenty of examples that disprove to the contrary. Philips on their FP56 and AA2, for example used reverse scan with an excider lamp as did Century with their R4 soundhead (it wasn't great but it was reverse scan with an exciter lamp...long before LEDs). The JAXLIGHT was a common forward scan LED light source, compatible with cyan dye tracks. There were even laser lights used too.

The chief difference is what is focused onto the cell. Was it the slit of light or was it the tracks themselves (with a slit used as a mask)? Even the direction of the scanning wasn't universal. As in, while some would think that forward scan has to do with the reader (Cell) being forward of the film (to the right)...Philips, again, put the exciter lamp on the right and the cell to the left of the film yet that would still be considered "Forward Scan" as it is projecting a slit of light onto the cell with all of the same alignments and characteristics of any other forward scan system.

Good to know forward and reverse existed with both lamps, LEDs and even other things like lasers. I was trying to describe a easy way to visually recognize one versus the other, but failed. How would you describe to a layperson how to easily know if their soundhead is a reverse or forward scan variety?

[Steve Guttag]

Just as I said...are you focusing the soundtrack onto the cell with a lens or are you focusing a slit of light onto the film?

[Ryan Gallagher]

Here is a visual reference for Dolby CAT 566 Uniformity Film.
Since Tony was so kind as to sell me his small selection. 566 was one of the loops I did not have in our kit until now.

Apologies for the crude light table, these have not made it to work yet.

IMG_6093.jpg

[Chris Wehrman]

Are any of the Dolby test films still manufactured?

[Tony Bandiera Jr]

I'll counter that CAT97, in the reverse scan era is of no use. There is nothing it does that other films can't do better. The only "measured" film is Buzz track. As such, that should set the film's lateral placement relative to the cell. CAT566 sets the films lateral placement to the LED as well as indicates if magnification is excessive (both high (right most) and low (left most) tones drop.

Without CAT566, CAT97 can be a poor-man's illumination film as it is supposed to be 100% modulation so if the waveform is clipped on either channel, your LED isn't centered or magnification is excessive if both ar clipped. In X-Y mode if the cross isn't perfect, it indicates uneven illumination too.

Naturally, for forward scan, then yes, CAT97 is needed to minimize crosstalk.

I will disagree to a point. The CAT 97 provides a more precise visual representation of the true lateral position to a degree that buzz track doesn't. Viewing the two CAT 97 signals on a scope you can get them centered (and offset) from each other EXACTLY in reverse scan, which means you are much less likely to clip one edge of either track on strong peaks. I have also had buzz track film in the past that varied from lot to lot in lateral precision.

I would also argue that buzz track isn't "measured" in the sense that Buzz track is normally used by listening, not by use with an oscilloscope.

Both are valuable in their own ways, and I still liked to use the CAT 97 as a follow up to the buzz track to make sure the lateral positioning of a reverse scan was as precise as possible. And since I always had the scope set up for azimuth anyways it only took less than a few minutes to cross check with CAT 97 anyways.

As for the illumination check, 97 isn't a good substitute for 566 as it is harder to interpret a distorted waveform that to simply see the level variations on an RTA. (And being a negative image it can suffer from false distortion from dirt or scratches worse than a normal image track.)

All that said, we will all have some differences in how we tackle A chain checkups and as long as the end result works, it doesn't really matter exactly HOW we get there.

Are any of the Dolby test films still manufactured?

Good question. I haven't looked at the current Dolby Catalogs...but since we are so deep into the Digital Age I would be surprised if they are still made.

[Steve Guttag]

Tony, what you miss is that Buzztrack itself is measured film and camera original...not duplicated (it's actually made in the same camera that shoots 35PA, it's one of the reasons it cost so much more than any of the Dolby manufactured films). I believe CAT97 is duplicated film and subject to the weave of every step in the printing process. And even if they record it for every foot, it isn't measured liked Buzztrack. If they disagree, Buzz track is correct CAT97 is not. It was never made to the tolerances of Buzz track. And, furthermore, if you don't have tone just outside of a dead centered cell with Buzz track, you are overscanning. If you have both tones, you are, obviously, underscanning.

I stand by that, for a reverse scan system, CAT97 is completely superfluous.

[Christos Gartaganis]

Cat. 97 is camera original negative, hence the light gray film base which is standard for both Kodak and Agfa sound recording films. All other Dolby test films were printed on Kodak Vision color print film

[Steve Guttag]

That is good to know (though I would call it more of a light purple than grey)...does the camera original use KS perfs over BH for the sound films?

[Christos Gartaganis]

All 35mm sound recording films (Agfa ST8.D, Kodak 2374 etc.) use the positive style KS-1866 perforation as the film has a continuous linear motion inside the sound camera. See below info copied from the latest Kodak product catalog:

KODAK Panchromatic Sound Recording Film 2374 / E / PSR683 / ESTAR Gray Base / 35 mm x 2050 ft roll / On Core / KS-1866

EASTMAN EXR Sound Recording Film 2378 / E / SRF668 / ESTAR Gray Base / 35 mm x 2150 ft roll / On Core / KS-1866