This is topic Optical sound technology in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.
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Posted by Ken Lackner (Member # 1002) on 01-11-2002, 11:48 PM:
The sound system is one of the systems I know the least about. Is there a good place to read about the various technologies used in reproducing optical sound?Why is reverse scan better than foward scan?
Why use red LED's?
What is a Jax Light?
Etc.... Is there one place where I can get the answers to these and other similar questions? Thanks!
Posted by Paul Mayer (Member # 355) on 01-12-2002, 12:25 AM:
Maybe start with Scott's FAQ in the Tips section...Paul
Posted by Ray Derrick (Member # 1001) on 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.
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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
Posted by Steve Guttag (Member # 268) on 01-12-2002, 09:08 AM:
There is also a wealth of mis-information too!Steve
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"Old projectionists never die, they just changeover!"
Posted by Ken Lackner (Member # 1002) on 01-12-2002, 11:14 AM:
I am at least vaguely into electronics because I am go to school for Electronics Engineering Technology. 
I should enjoy that article.I'll look around, and if I have questions, I'll ask.
Posted by Mark Gulbrandsen (Member # 72) on 01-12-2002, 11:25 AM:
Speaking of optical sound technology what ever happened to the laser based analog optical recorder that was being developed in Japan a number of years ago. I remember reading an article on it in an old SMPTE journal that had some amazing claims for it. As far as I know everything in use is still galvonometer based.
Mark @ GTS
Posted by John Walsh (Member # 168) on 01-13-2002, 12:12 AM:
Those old Cameron books about projection had a good section about (mono) optical sound.
Posted by Steve Guttag (Member # 268) on 01-13-2002, 12:37 AM:
The Audio Cyclopedia by Tremaine (sp?) though dated is still a good reference to start out with when learning about sound, including film sound.Steve
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"Old projectionists never die, they just changeover!"
Posted by Ray Derrick (Member # 1001) on 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.
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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
Posted by John Pytlak (Member # 331) on 01-16-2002, 09:32 AM:
John G. Frayne "wrote the book" on optical sound:"Elements of Sound Recording". Frayne Halley Wolfe. 1949
And numerous technical papers published by the SMPTE.
http://www.studio-sound.com/archive/may98/aes_timeline.html
http://www.kodak.com/country/US/en/motion/support/h44/h442.shtml
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John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion
Posted by Gordon McLeod (Member # 33) on 02-08-2002, 06:48 PM:
Mark here is a link to a current laser based recorder from a very high quality German firm MWA that also makes excellent dubbers http://www.mwa-studio.de/index2.htm
Posted by John Anastasio (Member # 607) on 02-08-2002, 07:00 PM:
I'd like to know how they managed to make a GREEN helium-neon laser. I'll be darned if I've ever seen one that color. Is there such a bird? I've seen plenty of green CO2 lasers, but never a HeNe that wasn't red.
Posted by Steve Kraus (Member # 476) on 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.
Posted by Mark Gulbrandsen (Member # 72) on 02-09-2002, 02:30 PM:
>What is a Jax Light? Jax Lights suck big time. They are a complete waste of time and you gain absolutely nothing from using one.
Mark
Posted by John Walsh (Member # 168) on 02-09-2002, 03:15 PM:
"Jax Lights suck big time. They are a complete waste of time and you gain absolutely nothing from using one."Sounds like a review worthy of being placed in the "Reviews" section! 
Posted by Dave Macaulay (Member # 813) on 02-09-2002, 04:31 PM:
Jax lights - you gain the ability to run a cyan track... if the "threat" ever materializes...Save the money, and get a real LED reverse scan kit when you really need it.
Posted by Mark Gulbrandsen (Member # 72) on 02-09-2002, 04:49 PM:
I am aquiring one in a trade in projector shortly. I may decide then to do a review. I always felt that they are a big scam!
Mark @ GTS
Posted by Steve Kraus (Member # 476) on 02-09-2002, 04:50 PM:
Since the JAX light results in output lowered sufficiently to require a pre-preamp you really do wonder how it would compare with simply staying with an incandescent bulb (which is rich in red) and adding the extra amplification. Throw a red gel in there if need be.
Posted by Gordon McLeod (Member # 33) on 02-09-2002, 08:02 PM:
Actually they are not as bad as some say I have installed many and only one of them had problems namely microphonics
I use them on the DP70 and am very happy with them and they are very cost effective
Posted by Tom Fermanian (Member # 1094) on 02-09-2002, 08:10 PM:
Jax Lights pretty good, use the in Philips/Norelco Kinotone DP 70 AAIIs & DP 75, very cost effective, running for almost 2 years NO problems 
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Posted by Steve Kraus (Member # 476) on 02-09-2002, 11:56 PM:
I don't know about the DP-75 but since the AA-II is already reverse scan it would make sense that all that is needed is an LED light source.
Posted by Mark Gulbrandsen (Member # 72) on 02-10-2002, 08:42 AM:
Well the JAX light in a DP-70 or DP-75 is the cheapskates way out of buying the real thing. There are now true LED reverse scan units available for both machines from at least two different companies!
Mark @ GTS
Posted by Steve Guttag (Member # 268) on 02-10-2002, 10:40 AM:
Mark,Did you make your reverse scan reader for the DP-75 as well? I know about the AAII version.
BTW, Steve K, the statement about the red LED being less of a service issue than the exciter lamp is not entirely true, especially not for all red LEDs...since they fade over time, they are constantly needing adjustment to ensure Dolby-Level. Also the LEDs often require a technician with suitable test equipment to install whereas the exciter lamp is changable by regular booth personell .
Steve
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"Old projectionists never die, they just changeover!"
Posted by Gordon McLeod (Member # 33) on 02-10-2002, 11:36 AM:
Actually with some of the crappy excitors out there now You need to a fair amount of playing around to get a even light out of some of them
Posted by Pete Naples (Member # 761) on 02-10-2002, 11:50 AM:
I've got some Jax lights here, four to be exact. 2 on a pair of DP70's and 2 on a pair of DP75's in the same cinema. It's interesting to compare the results between the two. On the DP70 the results are not at all bad, the being a projected image sound head the results are good to begin with, and as the cell is miles away from any stray light, the noise doesn't seem to be much od an issue. However on the DP75, totally different story. The guys can't have any lights on in the booth while running analogue, and we've had to become inventive with bits of cardboard to shield the cell from light reflected off the port glass.Walter Voight produces a version of his ACL for the DP70, which I am told gives stonking results, althoug I've not personally seen it. On the DP75 or FP20 it gives stonking results but can be a real pig to align, but it's worth the effort for the performance gained over tungsten or Jaxlight.
Gordon you are so right! FP20 / DP75 lamps seem to be the worst offenders, put it in, take it out, bend the flange, put it in, take it out, bend the flange some more........
Posted by Mark Gulbrandsen (Member # 72) on 02-10-2002, 03:47 PM:
Steve, Yes I did. I think BACP is also working on one, and they may also have a direct plug in replacement for the FP-20....no machining involved. By Bye JAX Light!
Mark @ GTS
Posted by Richard Fowler (Member # 893) on 02-10-2002, 05:46 PM:
The BACP RSTR 2000 fits the FP-20/30 units.....not as easy as doing a Century or Simplex per my tech but at least no machine work.
Richard Fowler
TVP-Theatre and Video Products Inc. www.tvpmiami.com
Posted by Tom Fermanian (Member # 1094) on 02-10-2002, 07:02 PM:
To some of you guys,Jaxlite may be a "cheapskate" way out, but alas our situation, each screen has Dolby Digital and a few DTS, so analog is used for back-up or some stray picture, or trailers without digital tracks, we found it more important to spend big bucks for digital sound than analog. BTW Ultra makes a cover box for DP75 to shield stray light, look into it.------------------
Posted by Mark Gulbrandsen (Member # 72) on 02-10-2002, 07:15 PM:
"BTW Ultra makes a cover box for DP75 to shield stray light, look into it." You've got to be kiddin. This deserves a full review as soon as I can get to it. Nothin like covern up the problem is there.
Mark @ GTS
Posted by Tom Fermanian (Member # 1094) on 02-10-2002, 07:52 PM:
JAXLITES for DP75s, yeah we know about them, we where the 1st one to purchase them, We found out about the stray light problem, Before, with no pre-amp and tungsten, NO PROBLEM, Now with LED and Pre Amp, Problems, These particular projectors have a full plexiglass door allowing light to seep in .So we built 2 metal cover in our shop, put one on machine, it worked, sent one down to ULTRA, they liked it and put it in production.
Again, cheapskates? well to your US Dollar, our Canadian Peso at 60cents "US" gives us the chance to pay 40cents more on each dollar for equipement bought outside Canada,(+ import,transport ,brokerage) you guys do the math? ------------------
Posted by Steve Guttag (Member # 268) on 02-10-2002, 07:55 PM:
>>"we found it more important to spend big bucks for digital sound than analog. BTW Ultra makes a cover box for DP75 to shield stray light, look into it."<<Then either get the BACP analog reader or the CE ASR-40 series reader...they are priced competitive to the JaxLight but at least give you something for your money other than noise.
Steve
Posted by Tom Fermanian (Member # 1094) on 02-10-2002, 08:04 PM:
Now we have a choice, 2 years ago, retrofitting with LEDS for DP75s, all we had available then was the Kinotone unit at $$$$$$$, or jaxlites ?? So instead of re-instaling tungsten, this was the economy way to go then, If any new retro's to come, we'll look in to other mentioned choices.------------------