Film-Tech Forum ARCHIVE: Checking Dolby Level

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Topic: Checking Dolby Level

Michael Brown
Phenomenal Film Handler

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

posted 10-08-2002 08:38 AM

CP-55 (without the SR card)

When I'm doing a routine check of the Dolby Levels using the test loop in the projectior. What formatt should the CP-55 be in.

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Brad Miller
Administrator

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

posted 10-08-2002 08:51 AM

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Ken McFall
Jedi Master Film Handler

Posts: 615
From: Haringey, London.
Registered: Apr 2001

posted 10-08-2002 09:56 AM

That's mono....

Newer runs of the Dolby Tone film have Mono clearly marked on them to avoid confusion.

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Manny Knowles
"What are these things and WHY are they BLUE???"

Posts: 4247
From: Bloomington, IN, USA
Registered: Feb 2002

posted 10-08-2002 10:13 AM

Actually, the format used in the test seems to be PROCESSOR dependent. According to the manual, the CP-45 wants to be in Format 04 (Dolby "A") when setting Dolby Tone.

See also "Hum in CP-45" for a Film-Tech discussion where this came up.

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Ken McFall
Jedi Master Film Handler

Posts: 615
From: Haringey, London.
Registered: Apr 2001

posted 10-08-2002 10:40 AM

Manny,

if you look at page 2.3 of the CP45 users manual it clearly states select format 01 Mono!!

All Dolby processors require you to setup with format 01 Mono as that's how the test films are calibrated.

There is a copy in the manuals section if anyone want's to check it out online.

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Gordon McLeod
Film God

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

posted 10-08-2002 11:30 AM

The CP45 must be in Stereo A as you will have interaction between the level pots since it appears that Dolby actually just shorts the LT and RT togather for mono

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Steve Guttag
We forgot the crackers Gromit!!!

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

posted 10-08-2002 12:03 PM

Now there is a piece of high-tech engineering that anyone would be PROUD of! <sigh>

Steve

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"Old projectionists never die, they just changeover!"

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Peter Hall
Master Film Handler

Posts: 314
From: London, UK
Registered: Dec 2000

posted 10-08-2002 12:09 PM

Looking at the CP45 there does seem to be a discrepancy in the owners and installation manual re what format to use - install says 04 owners says 01. Had a look at the cct to verify what was happening and it seems that on the Cat510 regardless of format LtRt (at the meter points) are fed together via some sort of buffer amps and then via an academy filter, meaning that the Acadamey mono out is there whenever you are running whatever format. It does not seem to connect the LtRt together. On further reading the manual it refers to a Cat240 - maybe I need a closer look inside a CP45 !

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Michael Schaffer
"Where is the
Boardwalk Hotel?"

Posts: 4143
From: Boston, MA
Registered: Apr 2002

posted 10-08-2002 12:40 PM

Does it really matter which format you chose? You set the gain of the optical preamplifier which comes before any circuitry for channel routing or NR. Or am I missing something CP-45 specific?
Michael

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Scott Norwood
Film God

Posts: 8146
From: Boston, MA. USA (1774.21 miles northeast of Dallas)
Registered: Jun 99

posted 10-08-2002 01:08 PM

What Michael said. Why would the format matter, since the preamp card is ahead of the format card in the signal chain?

(Having said that, I've always used format 01, since that's what the manual says.)

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Joe Redifer
You need a beating today

Posts: 12859
From: Denver, Colorado
Registered: May 99

posted 10-08-2002 02:42 PM

Hell I've always just stayed in Non-Sync. I have noticed no difference cycling between the formats. And yeah, the pre-amp card is before the format card so I don't see why it would matter. I'm sure someone is about to tell me that it is a life or death difference, though.

Note: I am using fabulous CP50's

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Pete Naples
Phenomenal Film Handler

Posts: 1565
From: Dunfermline, Scotland
Registered: Feb 2001

posted 10-08-2002 03:02 PM

Micheal, 01 Mono, the top button.

If you set it in 01, then leave the tone running and press 04 you probably won't see any difference on the Cat222 meters, if however you had an SRA5 or a Cat222 SR/A, and pressed 05 after setting level in 01, you would see a level increase.

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Ken McFall
Jedi Master Film Handler

Posts: 615
From: Haringey, London.
Registered: Apr 2001

posted 10-08-2002 04:00 PM

I have always used format 01 without any problems.

Our CP 45's have given faultless service for over five years. I'm sure if there was a problem it would have reared it's head by now. Our boards are the first issue from what I can see. Is it possible that a later issue had a design change relating to this.

Peter Hall would also have found fault if this was an issue as he installed quite a number of them for City Screen, all running faultlessly as far as I know.

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Steve Guttag
We forgot the crackers Gromit!!!

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

posted 10-08-2002 04:39 PM

The reason for using mono is to ensure that you are metering the pre-noise reduction and without any level compensation (3-dB for A and 6 dB for SR). Some meters are pre NR so it doesn't make any difference some are post NR (like the CP-50) so it does.

Steve

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"Old projectionists never die, they just changeover!"

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Paul G. Thompson
The Weenie Man

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

posted 10-08-2002 04:40 PM

Mono.

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