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Topic: Voices in the surround channel

Michael Brown
Phenomenal Film Handler

Posts: 1522
From: Bradford, England
Registered: May 2001

posted 10-13-2001 12:43 PM

We just installed Dolby. Its either a Cp 45 or 55. We run in Dolby A and I noticed a lot of the vocals also come from the surround as well as the front channel. Is this normal or is something wrong. It seemed to be the worst during Dude where's mt car. I suspect that the levels of the surrounds have been set too high anyway.

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Michael Brown
Bradford Student Cinema
www.Bradfordstudentcinema.co.uk

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Brad Miller
Administrator

Posts: 17775
From: Plano, TX (36.2 miles NW of Rockwall)
Registered: May 99

posted 10-13-2001 02:19 PM

It's either the azimuth of the optics in your soundhead, the Dolby level in the processor is off, or you have a defective matrix card (although very rare).

Out of curiosity, when there is straight dialogue in the track and everything else is dead quiet, do the leds on the noise reduction card bounce up and down "equally", or is one always higher than the other? Bear in mind the dialogue may be too low for this to register. It may take a scene with someone yelling.

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John Walsh
Film God

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

posted 10-13-2001 02:19 PM

For a quick test, you'll need to run a Dolby tone test film and verify the two channels are of the same level.

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Greg Pauley
Expert Film Handler

Posts: 173
From: Huntington, WV, USA
Registered: Jun 2000

posted 10-13-2001 03:05 PM

Since this is a new install, you might want to check the delay setting on the surround delay. Although, this sounds like you need to have the tech come back and check your a-chain again.

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Darryl Spicer
Film God

Posts: 3250
From: Lexington, KY, USA
Registered: Dec 2000

posted 10-13-2001 05:31 PM

depending on how high the surround levels have been set, you can get crosstalk in the surrounds.....have a feeling that the focus on the lens slit is out of adjustment causing loss of frequencies that will cause the matrix not to perform correctly.....the led's on the matrix should be at a minimum when setting the dolby tones correctly....if you can not get a minimume reading on the matrix then there could be a problem at the soundhead and A-chain.....

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Gordon McLeod
Film God

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

posted 10-13-2001 08:14 PM

It sounds like the azimuth of teh sound head is incorrect. This causes a phase difference between the two channels and that is how the surround channel is derived.
On the cat 150 the centre led should be bright the others should be effectively out when a cat 69t is running. Only UltraStereo has a led null bargraph on the matrix
Poor focus will actually degrade the surround channel not create false decoding since it will effect both channels equally.

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 10-13-2001 09:48 PM

I fully agree with Gordon.

I think a complete front end optic alignment should be performed.

Paul

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Randy Stankey
Film God

Posts: 6539
From: Erie, Pennsylvania
Registered: Jun 99

posted 10-14-2001 01:19 AM

I second the motion as well. But since there were already three people ahead of me that means I'm fourth.... So, I FOURTH that motion.

Get a complete A-Chain done on that projector.

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Ray Derrick
Master Film Handler

Posts: 310
From: Sydney, Australia
Registered: Sep 2001

posted 10-16-2001 09:23 AM

I fifth the motion! However there is one other factor to consider.

Most features these days are recorded in Dolby SR not Dolby A. The dynamic action of these two systems are quite different and incompatible. Also the left and right NR cards operate independently (they are not stereo coupled). So if you chose the wrong format, you will often experience an increase in surround dialogue leakage whenever music or effects are present at the the same time as dialogue.

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President
Panalogic Corporation Pty Limited
44 Carrington Road
Castle Hill NSW 2154
Australia
Phone: 61 (0)2 9894 6655
Fax: 61 (0)2 9894 6935

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Paul G. Thompson
The Weenie Man

Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000

posted 10-16-2001 03:15 PM

Very good point, Ray.

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Steve Scott
Phenomenal Film Handler

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

posted 10-17-2001 12:07 AM

I agree, the optics & a-chain need to be aligned. I've found that even on our CP500, when it runs coke trailers that were printed in SR in A-type, the dialoge gets flashed into the surrounds everyso often, it also seems to be a bit wavering between the front L & R channels.
I've read that while it is somewhat backwards compatible, SR alinged systems will only take advantage of the increased noise reduction & equalization if run with SR features. A-type just doesn't work well in these, as has been my experience.

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Michael Brown
Phenomenal Film Handler

Posts: 1522
From: Bradford, England
Registered: May 2001

posted 10-17-2001 10:09 AM

We do run in dolby A so it could be a SR/A incompatability problem. We are having the projector serviced on friday and they will look at the sound equiptment as well.

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Mat Overton
Film Handler

Posts: 4
From: West Yorkshire, UK
Registered: Oct 2001

posted 10-21-2001 08:15 AM

Can I just point out that the views represented above are those of our projectionist, and not those of the Bradford Student Cinema.

I am not aware of any problems with our sound system, and Mike has not been to see me regarding any issues with the surround channels.
I also know for a fact that the system was installed to the highest possible standard by our service engineer. The surround channels are operating at the correct level - which I saw for myself during the install. Also our service this week, was arranged specifically to sort out a problem with our projector, NOT our sound system. The optics are prefectly aligned, and an a-chain was completed which proved that the system is still running to the specified Dolby levels.
There is the correct delay between the front speakers and surrounds.
We are experiencing NO problems running SR films in Dolby A, and I have no doubts about the professional nature of our fitters.

Mat Overton,
Chairman
Bradford Student Cinema

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Gordon McLeod
Film God

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

posted 10-21-2001 12:41 PM

Well I would highly recomend that the Dolby Jiffy test be played through the system both the older "A" type version and the new SR version and verify that all is well. I doubt that a projectionist would post that they belive there is a possible problem unless they firmly believed there is one

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Steve Guttag
We forgot the crackers Gromit!!!

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

posted 10-21-2001 12:48 PM

Mat,

I was following along with your statements until you got to the part about having absolutely NO problems running Dolby SR films in A.

For starters...that is quite simply impossible. While both use a complementary compander system, they do NOT use the same filters nor dynamics. As such, your system has no choice but to mistrack both Lt and Rt channels in both level and frequency. Whereas the 2:4 decoder uses level and phase relationships to determine channel placement, it will also HAVE to mistrack from the orginal mix. Another problem is that SR uses what Dolby calls "spectural skewing" which to the layperson will mean, without genuine SR circuits, the signal will sound a bit bright without deep bass.

The effects of improper SR decoding cannot be overemphasised. Most, if not all, SR emulators don't track it well. Furthermore, your soundhead has to be in tip top shape for the SR circuits to not whack off the high-end. That is, with reverse scan soundheads, you should be fine, with forward scan, there will be some artificial HF attenuation, much worse so for 1 mil slits and taller.

If you don't have SR noise reduction, you should obtain it as soon as possible. If you do have it, you should use it.

Steve

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"Old projectionists never die, they just changeover!"

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