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Topic: Dolby Digital Drop out Problems

Michael Brown
Phenomenal Film Handler

Posts: 1522
From: Bradford, England
Registered: May 2001

posted 07-21-2001 07:25 AM

At a 16-screen multiplex I have started to visit often (Dolby Digital as the digital formatt in every screen) I have noticed that they have problems with Dolby Digital. At every reel change during the feature the audio drops to analoge and it seems to drop to analog between every trailer and the theatre logo/snipe also has the first second played in analog before if clicks into SRD. I also notices that the SRD dropped around 5 or 6 times during the creddits of Jurassic park 3.
Now does this suggest that they are simply making bad splices or is there something un-reliable about the SRD readers that they have installed as well.

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Michael Brown
Bradford Student Cinema
www.Bradfordstudentcinema.co.uk
"Do you snorkle?
No, I get nervous when brightly coloured fish stare at me face to face."

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John Walsh
Film God

Posts: 2490
From: Connecticut, USA, Earth, Milky Way
Registered: Oct 1999

posted 07-21-2001 09:29 AM

If it's happening in most of their auditouriums, I would guess they have not changed the digital reader "exciter" bulbs for a long time, or the service tech is aligning the readers wrong. (Is it an older theater complex? The first Dolby SR-D readers used a regular slide-projector like incandesent bulb, while the newer readers use a longer-lasting LED lamp.) Also, some basement SR-D readers are known be very difficult to keep in alignment.

Because of the rough treatment trailer and snipes get, the SR-D might not track cleanly between. But, it certainly should track for the 1-2 frames between feature reel splices with out dropping back.

When it went out during the credits (of JP3) did you notice anything that would indicate the film was damaged? Even if there were no splices, several feet of crinkled film might prevent getting a good reading. Many platter wraps occur at the end of a film.

Those are my guesses.

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Rick Long
Jedi Master Film Handler

Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999

posted 07-21-2001 11:52 AM

If you have the opportunity, you might get them to open the front panel of the Dolby (if its a 500 - externally observable if it's a DA-20) and observe the error rate. This is in the form of a red seven-segment led, and should read somewhere between zero (no errors) and 7 (imminent failure). A point after the number means + 1/2. "F" indicates unreadable track.

Often this can be caused by incorrect threading tension in the 700 or 701 soundhead, a build-up of splicing tape or dirt on the digital sound-drum or a sound lens in need of cleaning.

Just my two pence worth.

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Michael Brown
Phenomenal Film Handler

Posts: 1522
From: Bradford, England
Registered: May 2001

posted 07-21-2001 02:46 PM

As well as the drop out during trailers/snipes/reel changes It seems to to randomly drop out. I arrived to the auditoriun early and saw the credits for the previous performance as well as the credits for my performance.It seemed to drop out more the first time. There was no on-screen scratches ect to indicate damage.

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 07-21-2001 04:11 PM

Basement readers appear to be more prone to dropping out at a tape splice. If properly aligned though, the splice will run right through even with opaque tape, without a drop.

In addition to changing out the "exciter" lamp on the penthouse, if it is an led based reader, the level may very well have fallen causing the same problem.

However, assuming the reader is aligned adequately, the #1 cause for SRD dropouts is due to print shedding and the buildup of caked on dirt on the gate bands/trap. (The kind you have to scrape off with a flat head screwdriver.) Such buildup ends up making a nice scratch right through the SRD data track and voila, no more clean playback for the further life of that print, even though the picture may be flawless. This is where proper print lubrication comes into play.

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Michael Brown
Phenomenal Film Handler

Posts: 1522
From: Bradford, England
Registered: May 2001

posted 07-24-2001 05:57 AM

So I experienced the worst SRD problem so far at this theatre tonight.

The show started with the ads in analogue (and it sounded distorted and momo) also the picture didn't fill the screen and left a foot of black down the left of the screen. I went to the lobby and the picture was fixed immediately, but still the analogue sound. Anyway I gave it till the end of the ads and was about to go back to the lobby when I see this guy in uniform who looks like a projectionist stood next to the auditorium door. So I speak to him and say "It's stll in analog". So he says "How do you know its supposed to be in digital" and it went down hill from their and he told me that the digital processor was nackered so i looked like it was staying in analog so I sat down. Anyways right in the middle of the Swordfish trailer it pops into Digital. Then It pretty muched stayed in digital apart from about 2 occasion where it dropped for about a minute or 2. But just before the last reel change it dropps again and stayed in analog for the last 15 mins unit comming back in srd during the credit music.

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Michael Brown
Phenomenal Film Handler

Posts: 1522
From: Bradford, England
Registered: May 2001

posted 07-28-2001 08:09 AM

Swordfish in a small auditorium at this theatre last night. SRD dropped twice for about 5 minutes, the second time in very nearly made it out into the lobby. Also it had a Dolby Digital Surround EX tag before the feature, interesting since this is a small auditorium and I didn't think even the larger ones were supposed to have EX.

They also seem to only show dolby sound tags on scope films.

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Dave Macaulay
Film God

Posts: 2321
From: Toronto, Canada
Registered: Apr 2001

posted 07-28-2001 10:27 AM

We've had pretty good luck with the basement readers, the CE ones we have the most of need a bit of attention every few months to set the LED current as the LED does age and eventually fail. The LED is an array of quite a few tiny emitters, and they basically burn out one by one. Once this starts you need a new LED, as turning up the current just stresses the remaining ones more and they burn out faster... they generally last at least a couple of years for us though.
With the 700 the lamp is rated at 1500 hours but after 1000 or so it gets a but tired - the inside of the lamp envelope gets coated with something (probably evaporated filament) and the light gets poor.
The light pipe ends are very easy to damage, and repeated cleaning with even a q-tip affects them. Blowing off dust and occasional very gentle cleaning with a lens tissue is all you should ever need to do.
If you need lamps, call Gilson Technical Lamps - same lamp cheaper than from Dolby.
The biggest problem I've seen is print damage. Operators don't seem to know how to turn gate tension down, only up. We service a lot of Simplex Millenium machines and with the tension cranked up they can ruin the SRD info pretty quickly. If the guides happen to be nice and clean it's OK but they will always get a bit of splicing tape glue or other crap on them and that attracts dust - always abrasive dust. The digital "unquality" number just creeps up until SRD starts to drop out. Possibly if the processor is already doing a lot of error correction it will take a while to recover from a splice or other data interruption - it seems that if it's running at 2 or 3 it handles them perfectly but at 6 or 7 it'll drop to SR for a second or 4. Try to educate them on how to set the tension!

I've seen EX trailers running in houses that I know aren't EX. and SDDS, DTS, and SRD stuff in houses that are either analog or running a competing digital. With the quality of operators we have here now (licensing was dropped recently) I'm surprised when they get the feature reels in order and head up.... so having the right Dolby snipe is a lot to ask for.
Head office sends detailed lists of ads and trailers for each film and the stuff that belongs with a certain screen is probably forgotten when they do a move-down. If I was running 10 screens alone I think I might "forget" it too.

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Aaron Sisemore
Flaming Ribs beat Reeses Peanut Butter Cups any day!

Posts: 3061
From: Rockwall TX USA
Registered: Sep 1999

posted 07-28-2001 01:54 PM

>>Also it had a Dolby Digital Surround EX tag before the feature<<

There are logo trailers out now that actually SAY 'Dolby EX?' The only EX-encoded logo i know of is 'Rain' and that has the standard SRD logo on it.

Aaron

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Steven Pickles
Film Handler

Posts: 81
From: Gainesville, FL, USA
Registered: Mar 2001

posted 07-29-2001 01:46 AM

Aaron said: "There are logo trailers out now that actually SAY 'Dolby EX?' The only EX-encoded logo i know of is 'Rain' and that has the standard SRD logo on it."

The new 'Aurora' tag is also EX encoded, fyi. I don't particularly like that one though.... I would like to see a longer Dolby snipe--with all kinds of immersing sounds. That's just my opinion.

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Michael Brown
Phenomenal Film Handler

Posts: 1522
From: Bradford, England
Registered: May 2001

posted 07-29-2001 07:09 AM

It don't know the official name of the tag, but it does have to Dolby EX logo and not the plane Dolby Digital logo. There is also some text that is something like "the most advanced sound system" which appears before the logo.

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