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Topic: SRD Perf Delay

Kyle Connolly
Film Handler

Posts: 13
From: Ottawa, Ontario, Canada
Registered: Apr 2001

posted 07-30-2001 03:01 PM

Can anybody tell me how many perforations before a frame is the SRD info for that frame printed?

Thanks

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 07-30-2001 03:34 PM

Check out the Dolby site:
http://www.dolby.com/tech/m.ot.0006.FilmIndFAQ.html
http://www.dolby.com/tech/ac3flex.html

Since both "penthouse" and "basement" readers can be used with Dolby Digital, I suspect the sound leads the picture on the print by at least 21 frames. Does anyone know the exact offset?

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Eastman Kodak Company
Research Labs, Building 69, Room 7419
Rochester, New York, 14650-1922 USA
Tel: 716-477-5325 Cell: 716-781-4036 Fax: 716-722-7243
E-Mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

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Ken Jacquart
Film Handler

Posts: 82
From: San Francisco, CA, USA
Registered: Mar 2000

posted 07-30-2001 09:38 PM

The Dolby Digital data is printed 26 frames in advance of the picture (or 104 perfs).

ken

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 07-31-2001 07:28 AM

Thanks, Ken. Looks like 26 frames of sound need to be "protected" and not cut off when splicing together trailers --- i.e., don't remove the rating bands. Is there any way of looking at the Dolby Digital track with a magnifier and determining if the bits represent a modulated track? I've heard the presence of the tiny Dolby "Double D" trademark indicates valid data.

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Joe Redifer
You need a beating today

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

posted 07-31-2001 10:46 AM

I've never noticed a Dolby Digital perf withOUT a "double D". And I've studied at every single perf in exquisite detail.

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Steve Guttag
We forgot the crackers Gromit!!!

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

posted 07-31-2001 09:34 PM

" I've heard the presence of the tiny Dolby "Double D" trademark indicates valid data."

I'll bet it DOESN'T

Checking into trademark law....a trademark can not be functional or so sayeth my patent/trademark lawyer. If Dolby were to make the double-D logo a functional part of scanning the data...it would jepordize their trademark....I kinda doubt it.

Steve

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"Old projectionists never die, they just changeover!"

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Randy Stankey
Film God

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

posted 07-31-2001 09:47 PM

I thought the "Double-D" was how the processor registered successive images, just like those "bullseye" patterns that UPS uses to track packages with. In other words, if you know that the exact center of the image will always contain the same pattern of dots then you know how to find all the corners/edges of the data block.

I figure the registration could have been almost any pattern of dots, even a but since it was Dolby, why not make it the Dolby symbol. Not only would it be functional but it would instantly identify what you are looking at, if you were looking at it by eye. (Kinda' like the watermarks in the corners of TV screens that everybody hates so much.)

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Ken Jacquart
Film Handler

Posts: 82
From: San Francisco, CA, USA
Registered: Mar 2000

posted 07-31-2001 09:50 PM

Steve, you are correct once again. The presence of the tiny Double D in the block area does not mean there is data that represents audible audio... in fact, one day the Double D might not exist at all in the data block. Just think of what we could use all that extra space for !??

ken

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Brad Miller
Administrator

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

posted 07-31-2001 10:45 PM

My vote would go for a discrete EX channel.

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Jeffry L. Johnson
Jedi Master Film Handler

Posts: 809
From: Cleveland, Ohio, USA
Registered: Apr 2000

posted 08-01-2001 11:32 AM

Here's a Usenet posting by Roger Dressler from rec.arts.movies.tech.
http://groups.google.com/groups?hl=en&safe=off&th=b0a768d310c271af,19&start=10
From: SrrndHound (srrndhound@aol.com)
Subject: Re: logos in digital soundtracks
Newsgroups: rec.arts.movies.tech
Date: 1997/03/12

To end speculation, the [)(] logo in the center of the data block is just
a cute way to use leftover data space.

Consumer chips are now widely available, but they cannot decode the data
on Dolby Digital films. This is one more way we protected the system,
aside from patents.

Roger Dressler
Dolby Laboratories

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Danny Hart
Film Handler

Posts: 50
From: St Andrews, Scotland
Registered: Nov 2000

posted 08-01-2001 06:32 PM

I was told that Dolby were never going to use the middle of the area between perfs, being the part most likely to be scratched and damaged because it comes into the most contact with the sprockets. So they put their logo there instead. The optical line-up is achieved by a larger dot in each of the four corners and the square around the logo. The data surrounds it

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John Pytlak
Film God

Posts: 9987
From: Rochester, NY 14650-1922
Registered: Jan 2000

posted 08-02-2001 06:49 AM

Danny Hart said: "I was told that Dolby were never going to use the middle of the area between perfs, being the part most likely to be scratched and damaged because it comes into the most contact with the sprockets."

In my experience, damage to the area between the perfs usually originates at the edge of the perf, and not in-between. For example, excessive tension over a sprocket will "nick" the edge of the perfs. Projector abrasion tends to abrade or peel back the emulsion starting at the perf edge. Proper print lubrication and keeping the gate and intermittent shoe clean and free of rough spots or emulsion build-up helps prevent this kind of print wear. Also, use the lowest possible gate tension that still gives a steady image with good focus.

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