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This topic comprises 4 pages: 1 2 3 4
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Author
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Topic: Dolby Digital Readers.
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Scott Norwood
Film God
Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99
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posted 08-14-1999 09:24 AM
I don't know very much about aligning a Dolby Digital reader (I've read the CP-500 manual, but that's the extent of my knowledge), but the printed description doesn't make it sound any harder than a standard A-chain alignment. In some ways, it sounds like a simpler procedure.
Even a standard A-chain optical soundhead alignment isn't that difficult, particularly if you have a scope and a full set of test films. It's really just a "cookbook"-type procedure that can be done by anyone with a little technical knowledge and some patience. Of course, it helps tremendously if you have seen someone else do it beforehand.
It's even possible to do a fairly good job "by ear," using only the Dolby Tone/pink noise loop (been there, done that). It's really amazing what can be done with a Dolby manual, a bit of patience, a desire to do things "right," and the knowledge that management will never pay for a full set of test loops or a tech to visit the theatre.
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Scott Norwood
Film God
Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99
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posted 08-14-1999 11:20 AM
Gordon's point is a good one--maybe Brad should have a universal disclaimer so that we all don't have to have to worry about getting sued if we don't type "do this at your own risk" at the end of every post.
Of course, no one should be making adjustments to sensitive equipment without some knowledge of what he is doing and the consequences of misadjustment. If something works most of the time and is difficult to adjust, it's probably not worth the risk of making it worse. On the other hand, if it just plain doesn't work, then there's not much to be lost by experimenting.
Some of this also depends on the attitude of theatre management. Some places will call a tech to replace an exciter bulb. Others (like a certain place where I used to work) haven't had a tech visit in years. Obviously these are two extremes, but if you have someone who comes to your theatre every month or six months or year to align everything, it's worth being present to watch what he does and ask questions. Manuals are helpful, but are no substitute for seeing someone who's done the same thing dozens of times before.
Along the same lines, I recommend that all new projectionists try to seek out some "old timers" who have been in the business for decades. If you're lucky, you'll find one or two who are friendly and will enjoy having someone to talk to; learn everything you can about film care and projector maintenance from these people. In many cases the long-time union guys are the last of a dying breed of career projectionists, and it is worth learning from them before they are all extinct. Also, visit lots of different types of theatres; if you work in a platter house, visit a reel-to-reel booth; if you run a manual reel-to-reel setup, visit a gigaplex with platters and automation. Make an effort to understand how film is handled in different environments and what contributes to film wear and damage (and how to avoid it).
This forum is a great place to exchange information and ideas, both highly technical and general gripes about Technicolor reels and whatnot. Brad has done a nice job of gently moderating things (thanks!) without being overly intrusive.
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Bruce McGee
Phenomenal Film Handler
Posts: 1776
From: Asheville, NC USA... Nowhere in Particular.
Registered: Aug 1999
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posted 08-15-1999 11:31 AM
Back to self-aligment of the sound for a minute: When I got my Holmes, the seller shipped the lamps, lenses, and the sound slit lens in a separate container to "protect" them. Having messed up my share of 16mm junkers that I was experimenting with, I was not looking forward to a sound alignment. I found a reel of film that had alot of music on it, and went to it. Within 2 runs of the 20 minute reel, I had it pretty close to what I thought was clear, and true. A couple of months later, I found a few test loops on the net. I set it up using the headphones, and my meter (analog) I was not even close with my initial set ups. What a difference! Now, if my oscilliscope would only work again (very old dual trace B and K with no visible model #--case is missing--got hit by lightning while I was working on a TV--had no idea the storm was coming.) I could really tweak the alignment. For stereo, it s going to have to be perfect. Should I try to install the stereo cell that Brad sent me less than 1/8" from the running film? This will require some "engineering" on my part. You people are great. I have learned alot here. Bruce
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Scott Norwood
Film God
Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99
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posted 08-15-1999 05:41 PM
Bruce - interesting post. I certainly wasn't recommending aligning a soundhead by ear...I just said that it can be done, although you are definitely correct that a mono system is far less finicky than a Dolby system. Also, when you do the alignment you need to be sure that you are using a good print (i.e. not old, shrunken, cheaply printed trailers) with a well recorded track.
In my case, with a two machine booth, one projector's soundhead was aligned almost perfectly, which helped things tremendously when I had to replace the solar cell on the other projector. What I did was run the Dolby tone loop in projector #1 (good) and set the levels on the preamp card in the processor (CP-50). Then, I connected the second projector to the #1 input on the processor, ran the Dolby loop on that machine, and physically adjusted the solar cell to match the levels of the channels as closely as possible (optics were OK). I then re-connected each projector to its proper input and set the levels on the preamp card for the #2 projector. It wasn't perfect, but it only took about ten minutes, and sounded OK (the matrix was fine, though there was a little dialogue leakage in the surround channel).
Good luck. Another way to set things up by ear is to get a good mono print and adjust the optics and solar cell position while monitoring the surround channel (this, again, assumes a Dolby system). When you hear no information in the surround channel, check the left and right channels. If everything is aligned properly, the matrix will decode the mono information and play everything through the center channel only.
I'd be interested in hearing others' suggestions for low-budget soundhead alignment. I certainly wouldn't recommend that anyone try this unless the optics and/or solar cell are so far out of alignment that the situation can't possibly be made worse, which, sadly, is the case in way too many theatres.
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Rick Long
Jedi Master Film Handler
Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999
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posted 08-17-1999 12:59 AM
When you are alone in the booth and you know that the optical (or digital) reproduction isn't all it could be, there is a great temptation to try and see if you can improve the situation. If this temptation isn't there, you are in the wrong job.
Consider first, however, that the system once worked perfectly. Something has since changed. Taking the optical system as an example, (exciter-lamp, sound lens, latteral-guide adjustment and solar cell) think about what may have changed. In most projectors the sound lens is tightened down pretty well. It is not likely that it has shifted. Moving this lens can cause you an awful lot of grief. To properly align an optical sound lens requires a dual-trace scope, real-time analyzer, pink noise loop and two beers. (The beers are for consolation after you discover you have done a perfect A-chain alignment with the loop threaded with the emulsion on the wrong side).
Dolby puts out an excellent test film, the C.N. 251 "Jiffy". If you can convince your management to get you a copy of this film (please don't swipe it from your technician - he'll get even, believe me), it will show you more than you ever wanted to know about the quality of your sound system.
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