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Topic: Dialogue leakage in surrounds...help!!!

Michael Barry
Jedi Master Film Handler

Posts: 584
From: Sydney, NSW, Australia
Registered: Nov 1999

posted 09-03-2001 01:02 PM

I have a strange problem with (excessive) leakage in the surround channels in Dolby A/SR modes. It was suggested that the problem lies either with the azimuth of the soundhead or an imbalance in the levels between left and right channels. I found that the preamp settings were slightly out, but nothing drastic.

Oddly enough, the same problem exists with both projectors (on the same processor), and they have both recently had A-chain alignments done. Therefore, I am thinking that the problem lies with the processor side of things.

I made up a test roll consisting of a few film ads and trailers and ran these through both projectors with similar results. Then, I took the same roll of film to another auditorium with the same model processor (Panastereo CSP-1200) and the results were perfect - absolutely zero dialogue in the surround channels.

Logically, the problem is in the processor somewhere...but which card(s)/section? Thanks...

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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 09-03-2001 02:26 PM

If the projector's A-chain is properly set and the preamps are correctly adjusted for Dolby Level, the next culprit is likely to be the surround delay time. There should be some delay between the screen and surround channels for the surround effect to function properly. As I am unfamiliar with Panastereo units, I am sure that Gordon or one of the other PanaGurus can assist with setting this adjustment.

Aaron

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John Walsh
Film God

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

posted 09-03-2001 02:34 PM

I think Aaron pretty much right: It's most likely either A-chain or surround delay. Can you measure the crosstalk from the optical cell with LR buzz track? Since the A-chain was recently done, I'd suspect that first.

If you have a replacement preamp card, I'd try that, too. Although, I don't know much about Panastereo either.

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Steve Guttag
We forgot the crackers Gromit!!!

Posts: 12814
From: Annapolis, MD
Registered: Dec 1999

posted 09-03-2001 05:12 PM

i would try swapping the matrix decoder between the two units to see if the problem moves. I kinda doubt if it is the delay section.

Look at the SPI LEDs on the matrix decoder...the surround ones are the yellow ones at the bottom of the card....if you see them ghosting as the dialogue plays, then it is coming out of the decoder that way. Since you say it happens on both A and SR noise reduciton (different cards between the two) I would rule them out for causing a phase problem.

Again, since you have two units...it is a simple matter of swapping the cards to find the culprit.

Steve

------------------
"Old projectionists never die, they just changeover!"

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Gordon McLeod
Film God

Posts: 9532
From: Toronto Ontario Canada
Registered: Jun 99

posted 09-03-2001 09:16 PM

Check the back plane I had a case where the little switch for delay defeat had been switched to bypass for the delay
Also check the soundhead alignment since it appears the problem showed up after the alignment it is probably the culprit
thread up some cat 69 and see how much of it is leaking

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Michael Barry
Jedi Master Film Handler

Posts: 584
From: Sydney, NSW, Australia
Registered: Nov 1999

posted 09-03-2001 10:27 PM

I tried adjusting the surround delay setting but I didn't hear much difference...I will look for that delay defeat switch on the back that Gordon mentioned and try that again.

I'll try swapping the matrix decoder boards between the two units as Steve suggested and take it from there. Thanks again!

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Michael Barry
Jedi Master Film Handler

Posts: 584
From: Sydney, NSW, Australia
Registered: Nov 1999

posted 09-04-2001 02:48 PM

Thanks to everyone for their input. Everyone's suggestion was absolutely valid, but Gordon McLeod got it - it was the surround delay bypass switch, left on after the B-chain was completed. Also, the soundhead alignment has been re-checked, just to be on the safe side.

I must also add that it's a great privilege to have the designer of your sound processor personally come and do an A/B chain!

By the way, Gordon, Ray Derrick says hello...

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Patrick de Groot
Expert Film Handler

Posts: 161
From: Sprang-Capelle, Netherlands
Registered: Apr 2001

posted 09-04-2001 04:05 PM

It is almost certain that the L & R channels aren't set up to equal sound volume. We don't have (yet) a dolby decoder, but are using a cheap decoder (for home use). We are using a mixer to amplify the signal coming from the solarcell. If I listen to the surround channel true a headset while changing the gain of one of the inputs I can hear the voices. When put in the right stand all that remains of the voices are sounds as if someone is, well, let's discribe it as talking in a bathroom far away. You can't hear what they say!

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