I believe the infra-red LED's still work with high-magenta prints as there is still some silver content, but when cyan tracks final arrive, infra-red LED's will be as unusable as tungsten lamps.

I strongly suggest anybody with infra-LED's should be looking to upgrade to visible red LED's. Note that for the compenent engineering units with infra-red LED's this may mean a small mod to the power supply to correct the current supplied as they were original sent out a fixed voltage, other than that the upgrade is simple.

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Martin Dean

I strongly recommend not downgrading to visible red LEDs...it is a downgrade, afterall.

Steve

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NUMBER 1

Steve said, "Then there is the SMART NR circuit that is most likely mistracking to show off the problem (you will have the same problem with the Dolby CAT 222SR/A which is used in the CP-45 and lesser CP-65s)."

One of the "problems" I have found is that the reverse scan readers are, in a sense, TOO good. That is, thay have such an extended high frequency response that they pick up a great deal of very high frequency noise from the soundtrack. I doubt that most release prints have a useable frequency response to 13 or 14 kHz (if that high) and above that is just noise. Since the reverse scan readers read well past that frequency, the noise they pick up is likely to mess with the NR characteristics and produce strange results.

Now the SMART NR does a creditable job in playing SR encoded prints, but because of the simplicity of the design and the band splitting arrangement utilized, it is possible for excessive hf noise to cause sibilance problems due to mistracking.

Couple the excess noise with the slit loss compensation circuit characteristics, and you have a very real problem in some cases with some prints. The slit loss compensation is not needed for reverse scan readers. It is there to compensate for hf rolloff when using standard solar cell/exciter lamp soundheads. Reverse scan readers don't roll off the highs very much, so no compensation is needed. HOWEVER, the slit loss circuit is still there even when it is turned all the way down!!! It is a peaking circuit, and adjusting the slit loss control simply moves the frequency of the peak. When all the way down, the peak is at about 35 kHz, which is above the audible range, but is still low enough to possibly cause problems.

Tim, please contact me directly, and I will give you instructions on how to remove the slit loss circuit from your preamp card.

NUMBER 2

I saw this a while back, and I almost went crazy until I figured it out. Actually, I did not personally figure it out, but one of our good friends in Canada, (I think it was Eldon at King Cinemas) handed it to me on a silver platter.

He told me that if the LED source is even SLIGHTLY too far away from the film, you will get this kind of distortion. I had a customer in Michigan who was using MOD IIC processors (same preamp and NR as used in MOD IIBDIT) and had just upgraded to reverse scan readers and was having this problem. The problem was not there with the old soundheads. He was using Kinoton projectors as I recall, and he had to have a special mounting bracket machined so he could properly adjust the LED-to-film distance. It apparently was not adjustable in its original configuration. Once he got the distance set correctly, ALL the problems disappeared.

Hopefully this information will help you.

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Oscar Neundorfer
Chief Engineer
SMART Devices, Inc.

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As to the lack of need of slit-loss...perhaps but that would merely be a cover up of two problems...the incorrect light source (visible red) with a mistracking NR circuit. The problem isn't the slit loss. Fix the above two problems and the problem also disappears and with extended frequency response to boot. As to how wide a range the optical tracks have, one would have to ask the recording engineers as to what they are putting down.

Steve

That's not surprising. If the LED array is located too far from the film, the illumination of the track becomes more specular. It is therefore more prone to be scattered by the grains or any surface roughness of the film, affecting distortion, frequency response and noise level.

I have usually found it is best to put the PS in the rack and feed it off the same power as the processor

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http://www.autoramadrivein.com

I have never had to remove the slitloss circuit on a Mod2serries processor.
Also a compressor is really not needed if one is carefull about setting the levels

Optical soundtracks have a finite limit to the level that can be recorded since there is physically only so much width to the track. Full width is considered 100% modultion
Dolby cat69T is recorded at 50% modulation so one can set the levels to each transmitter so that it is impossible to overmodulate it by determining what input level is required for 100% modulation and then setting the input to it with the dolby tone running at half that amount

Most transmitters will sound a lot cleaner and less distortion done this way

Jim Alexander there are several problems in your method
First the RS mixer is unbalanced inputs so unless you have input transformer on each of the inputs that is probably one of the starting points for hum
second you need proper noise reduction of some form to correctly decode the encoded noise reduction in the LT and Rt optical tracks
third your equalizers should not be on the input of the matrix as you can introduce phase shifts (almost all graphs are phase shifting) which will cause false directional tracking of the matrix.
Also equaliztion is for speaker/room accoustics and that requires the use of an eq on the output to each channel

Almost all of the theatres that I have gone to that have these home brew system don't sound all that good and in fact several of them the old mono system was far less fatigueing (end of sermon put on flack jacket)

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Any closer will bring the individual elements of the LED array into focus, resulting in uneven illumination across the width of the soundtrack, causing amplitude distortion. Any further away will cause excessive magnification of the LED elements and more significantly, the gaps between them, likewise causing distortion.

Distortion caused in this way is a little different from the more familiar harmonic distortion (THD) or intermodulation distortion (IMD) in that it may cause more complex artefacts like splatter and sibilance.

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Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935

Daryl,
Putting in a JAX light in a drive in has no advantage at all over a reverse scan except for the lesser performance you will end up with. The JAX light preamp is inherently noisy itself and may have only added to the grief. Like most good techs will do, I've only installed one or two of them and then it was back to the real thing.

Mark