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Topic: Optical sound technology
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Ray Derrick
Master Film Handler
Posts: 310
From: Sydney, Australia
Registered: Sep 2001
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posted 01-12-2002 04:41 AM
There is a wealth of information available but it is spread from one end of the planet to the other. Unfortunately there is no one source that will tell you everything (someone should write a book).There is some info on the Dolby.com website regarding Dolby A and Dolby SR technology but you need to be at least vaguely into electronics to really understand it. Also there is an article on matrixing on the USLinc website under "Tech Forum" written by some guy called Morgan (mis-titled "The Digital Matrix" because it actually applies to the analog matrix), but it is not all that accurate in my opinion, but worth a read none the less. ------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
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Ray Derrick
Master Film Handler
Posts: 310
From: Sydney, Australia
Registered: Sep 2001
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posted 01-14-2002 01:09 AM
I agree with Steve, the Audio Cyclopedia is one of the best sources of good juicy information on not just optical and magnetic film sound, but on film and projection technology in general. Unfortunately it has been out of print since at least 1987 when it was replaced by the "Handbook for Sound Engineers - The New Audio Cyclopedia" which, although also an excellent reference, unfortunately contains none of the cinema-related topics. Both books are also very thick (about 3") and very expensive. ------------------
Ray Derrick
President/Chief Engineer
Panalogic Corporation Sydney, Australia
Phone: 61 (0)2 9894 6655 Fax: 61 (0)2 9894 6935
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Steve Kraus
Film God
Posts: 4094
From: Chicago, IL, USA
Registered: May 2000
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posted 02-08-2002 09:26 PM
Ken Lackner asked:
>Why is reverse scan better than foward scan?Reverse scan is the term used when the image of a soundtrack is projected onto a slit in front of the light sensitive element (generally a solar cell) as opposed to the previously more common method of focusing the sliver of light from a slit onto the track. There have been soundheads using this system for many years. The reason it's better is that (generally speaking) they give much better frequency response and on a stereo installation have an almost complete absence of crosstalk between the channels. >Why use red LED's? Why use LED's? Because they don't usually burn out and their output declines only very slowly both of which mean less maintenance is required. Why RED? Because of a threat that the industry will convert to a soundtrack that exists entirely in the cyan dye layer of the film. Current soundtracks are specially processed to retain the silver normally removed in developing so that the dark part of the track will be opaque to infrared light, which is the bulk of what a conventional incandescent bulb puts out. (Processed color film is otherwise almost totally transparent to IR.) The early versions of the modern LED-based reverse scan systems used IR LED's. >What is a Jax Light? JAXLight is a product of Ultra Stereo (USL Inc.). It's a red LED assembly that plugs directly into the conventional exciter bulb socket. Output off the solar cell is lower so they include a booster amp to be installed in the audio lines. It does not give the benefits of a reverse scan retrofit but it does make the soundhead compatible with the threatened cyan tracks and also reduces maintenance since it's an LED.
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I should enjoy that article.
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