Some months ago the Astor cinema in Melbourne (Australia) had some new prints run off in LA of some old movies for a film festival. When they took delivery of the prints they tried running them on their red-LED reverse scan soundhead and the sound was low level, distorted and "harsh". In fact so much so, that they were unable to run them for the public. As it transpired the soundtracks were variable density and had been printed in high magenta. A tech was called who converted the soundhead back to the old exiter lamp setup and the prints played perfectly.

So it would seem that high magenta, a red light source and variable density do not mix. I have since wondered what would have happened if the variable density track had been printed in cyan, or if the high magenta track had been played with a high intensity green light source(green being complimentary to magenta). I suspect that the problem is due to the "grey scale" of the variable density track being rendered non-linear by the red light source.

Anyone else come across this problem and/or any technical explanations for the problems experienced by the Astor?

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Ray Derrick
President
Panalogic Corporation Pty Limited
44 Carrington Road
Castle Hill NSW 2154
Australia
Phone: 61 (0)2 9894 6655
Fax: 61 (0)2 9894 6935

I would suspect that if you changed the LED to an infrared one that the film would have played ok as well.

I have one exhibitor that is having me do just that and we will experiment. I also believe that the motion picture academy theatre has infrared LEDs rather than the visable ones to handle all of the soundtracks best (cyan not a reality yet, and probably never).

The whole red LED thing just ticks me off every time. It is a dumb idea in this day and age that yeilds inferior results at best. Their life-span is a bit wild too and their fading is unacceptable. All of the infrared LED systems we have installed since about 1996 are still running and still at Dolby level without having to constantly tweek them (over 12000 hours later)...you can get a red LED to say constant for even a month.

Steve

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Steve, interesting point about infra-red LED's. The tracks may have played correctly if that option was tried. I also agree that the rate of fading of red LEDs is unacceptable. Have you run any cyan film with an infra-red system? In theory, primary red light (approx 650nm) should produce the greatest degree of "darkness" of cyan dye, so infra-red (theoretically) will produce less contrast and hence lower gain and higher film noise. But as you say, the peak sensitivity of solar cells is in the infra-red region (about 7dB better at 950nm than at 650nm to be precise) so this will tend to offset the gain loss but not the increased film noise. I look forward to the results of your tests.

John, the matter was reported to several "authorities" on the subject at the time, including Jesse at UCLA, but as far as I am aware, no one has come up with an actual technical explanation for the distortion and harshness at this time.

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"Unfortunately, the dyes used in all color prints have a very low absoption in the infrared region."

They go on to discuss Fig 2 of the document, which shows very little absorption in the infrared region when silver re-development is not used. In other words, cyan dye (or any other colour dye) is largely transparent to infrared light in the absence of silver.

This patent makes interesting reading and can be found on the US Patent Office website (www.uspto.gov) The patent is essentially for the use of a red LED to read a cyan analogue soundtrack. Yes folks, Dolby have actually patented the colour RED!

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Ray Derrick
President
Panalogic Corporation Pty Limited
44 Carrington Road
Castle Hill NSW 2154
Australia
Phone: 61 (0)2 9894 6655
Fax: 61 (0)2 9894 6935

Since converting the main (smaller) screen to Red LED, I've rarely found problems with older B&W films...
I tend to get the most complaints from pensioners, who want to hear the dialogue, and none of that music... can you ask the projectionist to turn it off...

Incidentally, we play host to the local film society, and their head honcho is a pensioner... They insist we show films 'right' and have often asked for the volume to be turned up if they feel it's too quiet...

Sometime's I'm glad not to be in a multiplex chain, though I'd love to have any form of Digital sound in the main screen.....

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Every christmas, someone somewhere plays 'It's a wonderful life', every christmas I will get a barrage of calls from managers and projectionists who haven't dealt with this film before. Somewhere in reel three is a noise, not unlike motor boating, we never heard it with exciter lamps, but we sure as hell are hearing it now with reverse scan LED! To be fair this is a reprint (but not a new reprint) copy that does the rounds at Christmas.

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