Film-Tech Forum ARCHIVE: Dolby Digital Sound Problem

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Posted by Mike Lauber (Member # 1486) on 07-06-2004, 10:34 PM:

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.

Posted by Richard Hamilton (Member # 321) on 07-06-2004, 10:41 PM:

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

Posted by Mike Pennell (Member # 1692) on 07-06-2004, 10:43 PM:

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]

Posted by Mike Lauber (Member # 1486) on 07-06-2004, 10:47 PM:

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.

Posted by Rick Long (Member # 213) on 07-06-2004, 10:55 PM:

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.

Posted by Richard Hamilton (Member # 321) on 07-06-2004, 11:12 PM:

Can you listen to processor output on the monitor speaker?

Posted by Mike Lauber (Member # 1486) on 07-07-2004, 01:35 AM:

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.

Posted by Richard Hamilton (Member # 321) on 07-07-2004, 01:39 AM:

How does it sound in different formats? What kind of processor, monitor, amps and speakers?

Rick

Posted by Steve Scott (Member # 630) on 07-07-2004, 02:13 PM:

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.

Posted by Gordon McLeod (Member # 33) on 07-07-2004, 03:16 PM:

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

Posted by Mark Gulbrandsen (Member # 72) on 07-07-2004, 08:19 PM:

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

Posted by Mike Babb (Member # 1379) on 07-08-2004, 04:02 AM:

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.

Posted by Dean Kollet (Member # 1789) on 07-09-2004, 12:27 PM:

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...