Film-Tech Forum ARCHIVE: voice/dialog on surround channel,how and why it happens?

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Posted by Luciano Brigite (Member # 1104) on 08-17-2004, 10:39 PM:

Hello,
Well, I believe the title speaks for itself but recently I'm having
some problems im keeping voices and dialog away from the surround channel,from 6 theatres, only two will work ok, the others or will have some voice leak or then the surround will act the same way as the center. in these theatres the processor (?) is the same, Starscope on all the 6. with the exception of one theatre that has a bad sound reproducer ( cell is a bit far from the film and can't be moved because some moron instead of looking for a screw to hold the cell assembly in place,wrapped it with electrical tape and hammered it into the main assy now it can't be taken off unless some "special care" is used for it), the others had the A chain redone from start ,two had it done twice , from the 5 remaining theatres, 2 had it fixed with the A chain but the others,no matter what is done keeps "talking" tru the surrounds. I'm considering a fault in the main card of those starscopes ( BTW.. the reason I dislike them is because of the way it handles the surround channel) or a messed up calibration in one of the trimpots inside or then shorted IC's or anything else. I downloaded and read the manual for it and followed the steps from it but no result. Am I missing something in all this?
in case the problem lies with the main card, who'd be the culprit? (sp..?)

thanks! [Smile]

Posted by Jack Ondracek (Member # 1466) on 08-17-2004, 11:58 PM:

It's a shame that Paul isn't around to answer this, because he was "blessed" with keeping one of those thing running for a long time after I installed it.

From my recollection of that system though, you really need to find a way to stabilise your pickup cell. If you can't set your optics properly so the phase alignment is dead on and locked down, and separation between the channels is as good as you can possibly attain, that box will forever be a problem. For that matter, analog surrounds are driven by the phase relationships of the two channels, so proper phase and level alignment is necessary, regardless of what processor you've got running in your booth.

I don't remember... does the Starscope have surround delay? If not, you may be relegated to aligning your system as well as you can, then monitoring the surround levels judiciously so as to keep that leakage to a minimum.

I service an old CP50 that's pretty picky about the same factors.

Posted by John Hegel (Member # 628) on 08-18-2004, 12:21 AM:

I had the same type of problem on an old Smart processor.

For me the simple but most likely incorrect fix was to play with the Left and Right gain from the cell until the dialog in the surround was gone.

I'm not saying it was the right way to fix it, but it worked.

Posted by Darryl Spicer (Member # 711) on 08-18-2004, 12:25 AM:

The below link may help and it does have some of Pauls wisdom within it.

Eprad Starlet/Starscope crosstalk

Posted by Gordon McLeod (Member # 33) on 08-18-2004, 09:53 AM:

There is a phase detector gate and one should see the phase led light as the relative phase of the two channels deviates and that will control the amount of the L-R signal that gets to the surround output
The bottom line is that it is essential to have the most accurate azzimuth alignment for it to work at all

Posted by Luciano Brigite (Member # 1104) on 08-18-2004, 01:03 PM:

There is no delay in the surround channel on the starscope ,most of the "matrix" board of it is taken by the surround channel and there's no delay Ic's on it nor a double card like the Dolby's matrix) playing with left and right gain isn't really an incorrect fix, if I'm right, starscope's manual mention it at some point and was some of the things I did try with the faulty ones, now that was mentioned here, there is a gain problem with two of them, one of the channels needs to be set at full while the other goes all down but is still higher than the other and with one other,along with the same gain problem described above,the cell is saturating the pre-amp inputs even with the exciter running low ( 8,5V -4A exciter running at 5V)
During all these years I deal with theatre,since when I started as a projectionist to nowadays as a (wannabe) tech, only two or three times I saw that phase led going lit, all the others it was always off but even that way there was surround in the auditorium with or without voice leak.
It has annoyed me quite a bit that I'm going to build it's matrix card to carry around and make things easy next time I face one of these talking tru every channel or doing "funny things" .

maybe I should have badmouthed the starscopes a lot less.. now they're taking revenge on me [Embarrassed]

Posted by Gordon McLeod (Member # 33) on 08-18-2004, 01:25 PM:

There are two LEDs one is labeled threshold and the other is phase
The thresold pot is accessable externally and the phase level is internal
I it stays on all the time I suspect the LDR has failed on the board as it is the actuall device that does the gateing
Also if there is a gross input level position difference there is a balance pot that will help
Also check and make sure that the slit loss pots are set approximately in the same position as they can cause phase errors