Film-Tech Forum ARCHIVE: CP-500 Dolby level, which would you trust?

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Topic: CP-500 Dolby level, which would you trust?

Rick Long
Jedi Master Film Handler

Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999

posted 04-27-2002 12:15 AM

In more than one situation, when running C.N. 69T tone loop to adjust optical Dolby level, I get disagreement between the CP-500 screen and the red/green leds on the 222/SRA card.

This has happened in maybe 5% of the units i have aligned.

Perhaps because of being used to the CP65's, I tend to trust the card.

Which would you trust?

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Steve Guttag
We forgot the crackers Gromit!!!

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

posted 04-27-2002 12:24 AM

The meters on the Cat. 222SR/A are supposed to be calibrated, individually (I belive Dolby calls it "AOT"). Thus, they should be right. I would trust them first. I also tend to press the SR format and look at the level meters on the LCD screen and make sure the Left and Right meters are moving about equal.

Steve

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

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Pete Naples
Phenomenal Film Handler

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

posted 04-27-2002 04:42 AM

I've noticed this too, and being a ludite in these matters I use the LED's on the 222 SR/A, ok it's awkward holding the door open and twiddling the fader, but what the heck.

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Rick Long
Jedi Master Film Handler

Posts: 759
From: Toronto, Ontario, Canada
Registered: Nov 1999

posted 04-28-2002 04:23 AM

Agreed that it is a pain holding open the CP-500 door while operating the fader to achieve the proper settings for the 222 SR/A card, it is more difficult still, when one realizes that the cause of this lost gain is due to a slowly fading led in the sound-head (bright red 770 nanometer type).

The sound system rack sits against the front wall of the booth, to the right of, and facing the projector head, making the leds on the 222 card invisible to the poor sod adjusting the exciter level from behind the projector.

The only response is to close the rack, squint at the front panel and increase the exciter gain until the front panel agrees that the level is about close to, or slightly over the needed setting and then check the veracity with the internal 222 card.

This begs yet another question; where is the proper comprimise between led level (adjusted to get maximum life from the exciter) and Dolby level settings (as given by the sometimes inaccurate front panel reference) to acheive Dolby level?

Although I can get Dolby level with the gain indicators anywhere from 3/4 to full-up, it has always been my experience that running any system at full gain is undesirable (due to excessive pre-amp noise, ect.).

In short, where would you suggest is an ideal spot for the gain controls (in fractions of full-gain) to be set?

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