Film-Tech Forum ARCHIVE: Warbled Sound

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Posted by Joseph Muggio (Member # 4013) on 10-14-2006, 01:47 PM:

I have a problem with warbled sound. It sounds worse during music than dialogue. I am running a Simplex PR-1006 proj. with an SH-1000 series (Four Star) modified to red. Any ideas from anyone what could be causing this and how can I fix it? Could this be a simple misalignment?

Posted by Gordon McLeod (Member # 33) on 10-14-2006, 03:53 PM:

I would suspect it is the rubber (or felt) section of the pinch roller in the sound head lateral guide roller has a flat spot

Posted by Mark Gulbrandsen (Member # 72) on 10-14-2006, 06:56 PM:

Check.........

The sound drum to be sure it spins freely and does not bind at all. Get it spiinning and then it should slowly decelerate over 20 to 30 seconds.

That the upper half of the lateral guide roller that you close over the sound drum pivots easily at it's hinge point or knuckle... if its stuck this can cause a lack of contact and may result in flutter.

That the upper casting of the lateral guide roller arm is not cracked in any way, I replaced 4 of those castings that were cracked last week!

The impedance roller and its associated bearings are in good shape as Gord suggested. Also the inner half away from the sound track of the lateral guide roller is spring loaded and when you push it open it should go back to its normal point immediately.

Hope some of this helps....

Mark

Posted by Bill Enos (Member # 440) on 10-14-2006, 07:01 PM:

Before going with any of these disaster scenarios, check the drum and the roller for anything even slightly sticky, tape, tape residue, etc. Seen this a few times, never found anything broken.

Posted by Mark J. Marshall (Member # 1409) on 10-14-2006, 07:51 PM:

Check to make sure that the pinch roller, when in the closed position, is actually holding the film onto the sound drum and not letting it slide through freely. I've seen that problem before. Not only resulting in warble, but also some faintly scratched prints.

Posted by Frank Dubrois (Member # 3042) on 10-15-2006, 01:18 AM:

I heard pulling the film to tight before snapping the rollers closed could cause that also.

Posted by Joseph Muggio (Member # 4013) on 10-15-2006, 12:03 PM:

I won't be able to check these things again until Friday when I'm at the theatre again. For a single screen, we only run weekends, but I'm usually there well before the doors open. Will post again after that. Thanks to all for your input.

Posted by Gordon McLeod (Member # 33) on 10-15-2006, 03:01 PM:

Also I assume you are threading it correctly with 2-3 perfs of slack film across the scanner

Posted by Bob Koch (Member # 1062) on 10-15-2006, 03:30 PM:

After you checked the things that have been suggested;take the lateral guide roller apart by taking the "bristo" setscrew out and separating the top and bottom of the roller by pushing the pivot pin out and removing the spring behind the tension ball and retensioning it[stretch]This will probably do it. Make sure neither of the "pot metal" castings hasnt cracked, as this will most certainly cause the problem you mention.

Posted by Joseph Muggio (Member # 4013) on 10-21-2006, 06:52 PM:

I've checked everyone's suggestions. I found no broken or cracked areas on the pad roller arm, but have found that the support shaft bearings may be the cause. As for the lateral guide roller, there seems to be no flat spots. Are lateral rollers supposed to side-to-side motion and how much? The drum itself also has some side-to-side movement when gentle pressure is applied. The red light bracket is only a millimeter or two from the edge of the drum. It now seems that the warbling sound is more defined. Anything else I can do short of calling the tech in?

Posted by Floyd Justin Newton (Member # 1316) on 10-21-2006, 07:03 PM:

Makr sure that NOTHING is touching the flywheel (cableing and etc) as this will surely cause "wowing".

Posted by Joseph Muggio (Member # 4013) on 11-05-2006, 01:12 PM:

I just wanted to let everybody know that most of our sound problems have (for the most part) been corrected. It turns out that the CAT 222 gain controls were set way too high causing distortion. The CAT 240 card showed only red LED's on both l/r channels. Now it sounds a lot better with just a faint distortion. It was also recommended that I change the rubber roller and bearings on the lateral guide roller, which after being removed, I'll have to run buzz track to realign. Does anyone have any further suggestions??

Posted by John Hawkinson (Member # 1135) on 11-05-2006, 06:17 PM:

What processor is this?

In any case, it sounds like you should run dolby tone and set the gain based on that. Have you done so?

--jhawk

Posted by Joseph Muggio (Member # 4013) on 11-06-2006, 09:40 AM:

The gain settings we made were done using Dolby tone.