Film-Tech Forum ARCHIVE: SRD Perf Delay

This is topic SRD Perf Delay in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Kyle Connolly (Member # 827) on 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

Posted by John Pytlak (Member # 331) on 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

Posted by Ken Jacquart (Member # 369) on 07-30-2001, 09:38 PM:

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

ken

Posted by John Pytlak (Member # 331) on 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.

Posted by Joe Redifer (Member # 3) on 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.

Posted by Steve Guttag (Member # 268) on 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!"

Posted by Randy Stankey (Member # 64) on 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.)

Posted by Ken Jacquart (Member # 369) on 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

Posted by Brad Miller (Member # 2) on 07-31-2001, 10:45 PM:

My vote would go for a discrete EX channel.

Posted by Jeffry L. Johnson (Member # 453) on 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

Posted by Danny Hart (Member # 659) on 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

Posted by John Pytlak (Member # 331) on 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.