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Author Topic: Dolby Digital Sound Problem
Mike Lauber
Film Handler

Posts: 19
From: Fond du Lac, WI, USA
Registered: Nov 2002


 - posted 07-06-2004 10:34 PM      Profile for Mike Lauber   Email Mike Lauber   Send New Private Message       Edit/Delete Post 
I suddenly am having a problem with the sound in one of our Dolby Digital Theatres. The center channel sounds fuzzy and crackly throughout the entire movie. The rest of the channels sound fine. Is this likely a problem with that amp? The Digital Processor shows it's reading the digital track fine. It just started happening today, so I haven't tried any other prints, but it did it through the trailers and all reels. Thanks in advance for any help.

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Richard Hamilton
Phenomenal Film Handler

Posts: 1341
From: Evansville, Indiana
Registered: Jan 2000


 - posted 07-06-2004 10:41 PM      Profile for Richard Hamilton   Email Richard Hamilton   Send New Private Message       Edit/Delete Post 
How does the movie sound in "bypass" mode, or SR, or mono? If it sounds the same, I would suspect a blown speaker. What kind of amps and speakers? Since you said it happened during all of the previews and all reels, it's not a print problem.

Rick

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Mike Pennell
Expert Film Handler

Posts: 150
From: Tucson, AZ, USA
Registered: Apr 2003


 - posted 07-06-2004 10:43 PM      Profile for Mike Pennell   Email Mike Pennell   Send New Private Message       Edit/Delete Post 
Possible bad amp, speaker, high frequency diaphram, or loose connection. Check your wires coming out of the amps and into the speaker and make sure they are tight. Hows the dialog sound? Real Bassy? then check your diaphram. You could try trading the outputs between either left/right and center to check the amp. Make sure you mark them and put them back correctly. [beer]

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Mike Lauber
Film Handler

Posts: 19
From: Fond du Lac, WI, USA
Registered: Nov 2002


 - posted 07-06-2004 10:47 PM      Profile for Mike Lauber   Email Mike Lauber   Send New Private Message       Edit/Delete Post 
It sounds poor out of the Amplifier Monitor Speaker too, so I don't think it could be the speaker. I haven't tried it in bypass or in SR at all yet, but I will later tonight. The dialog doesn't sound bassy, just fuzzy.

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Rick Long
Jedi Master Film Handler

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


 - posted 07-06-2004 10:55 PM      Profile for Rick Long   Email Rick Long   Send New Private Message       Edit/Delete Post 
Try the re-set button on the Dolby if your unit has that feature.

Otherwise, exchange the wiring for the left and centre amps to see if the problem travels.

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Richard Hamilton
Phenomenal Film Handler

Posts: 1341
From: Evansville, Indiana
Registered: Jan 2000


 - posted 07-06-2004 11:12 PM      Profile for Richard Hamilton   Email Richard Hamilton   Send New Private Message       Edit/Delete Post 
Can you listen to processor output on the monitor speaker?

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Mike Lauber
Film Handler

Posts: 19
From: Fond du Lac, WI, USA
Registered: Nov 2002


 - posted 07-07-2004 01:35 AM      Profile for Mike Lauber   Email Mike Lauber   Send New Private Message       Edit/Delete Post 
Yeah, you can on the monitor, but for some reason nothing comes through when I listen to it on 'processor'. It used to always work fine, and it still does in our other dolby digital theatre.

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Richard Hamilton
Phenomenal Film Handler

Posts: 1341
From: Evansville, Indiana
Registered: Jan 2000


 - posted 07-07-2004 01:39 AM      Profile for Richard Hamilton   Email Richard Hamilton   Send New Private Message       Edit/Delete Post 
How does it sound in different formats? What kind of processor, monitor, amps and speakers?

Rick

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Steve Scott
Phenomenal Film Handler

Posts: 1300
From: Minneapolis, MN
Registered: Sep 2000


 - posted 07-07-2004 02:13 PM      Profile for Steve Scott   Email Steve Scott   Send New Private Message       Edit/Delete Post 
What processor are you using? Is this a DA10/DA20 or a CP500D/CP650D, or some other combination? You may need to do some modification to the cards to eliminate the problem, expecially if it's high frequency distortion.

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Gordon McLeod
Film God

Posts: 9443
From: Toronto Ontario Canada
Registered: Jun 99


 - posted 07-07-2004 03:16 PM      Profile for Gordon McLeod   Email Gordon McLeod   Send New Private Message       Edit/Delete Post 
Since the problem wasn't there before it is something that has failed so modification isn't the needed reedy but repair
I find it odd that also sudenly the monitor has no signal present when in monitoring processor out mode
My bet is that the speaker has had an issue and is damaged
Is the system Biamped
Try as Rick sujested to play in analogue and see i the problem persists

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Mark Gulbrandsen
Resident Trollmaster

Posts: 16113
From: Bountiful, Utah
Registered: Jun 99


 - posted 07-07-2004 08:19 PM      Profile for Mark Gulbrandsen   Email Mark Gulbrandsen   Send New Private Message       Edit/Delete Post 
Actually Dolby has had quite a few mods that can be done in the field to the DA-20 / CP-500. In fact the latest CP-500 Dolby mod is to eliminate random clicks heard in all the channels on some CP-500s. We did have one customer that had bad problems with clicks and the mod solved the problem in all the processors Its caused by a bad clock. Most mods however are done only by Dolby because it involves software and can only be had by purchasing a new revised board for what ever it may be.

Mark @ CLACO

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Mike Babb
Expert Film Handler

Posts: 227
From: Norwich UK
Registered: Jul 2002


 - posted 07-08-2004 04:02 AM      Profile for Mike Babb   Author's Homepage   Email Mike Babb   Send New Private Message       Edit/Delete Post 
I've heard this type of thing with a bad gain pot on the amp, the tests suggested above should sort it out for you if so.

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Dean Kollet
Jedi Master Film Handler

Posts: 591
From: Florida State University
Registered: Jul 2003


 - posted 07-09-2004 12:27 PM      Profile for Dean Kollet   Email Dean Kollet   Send New Private Message       Edit/Delete Post 
I don't know if you are using a Dolby Analoq processor as well, but we had the same problem last night running a movie. The fix that usually helps me (and I don't know if you are set up this way) is to shut the entire sound rack down and pop our our crossover cards and put 'em back in. It has helped 9 times out of 10, loose connections kill you.

More info on your equipment will help a lot too...

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