Film-Tech Forum ARCHIVE: Digital Offsets

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Posted by Mark J. Marshall (Member # 1409) on 11-04-2002, 02:35 PM:

Does anyone know the offsets of the DTS, SDDS and SR*D digital tracks on 35mm?

Thanks in advance,
Mark

Posted by Bill Gabel (Member # 1105) on 11-04-2002, 02:40 PM:

On what type projectors? And penthouse or basement readers?

Posted by Adam Martin (Member # 641) on 11-04-2002, 02:48 PM:

I think he means on the film itself where the soundtrack is in relation to its corresponding image area, like the analog offset.

Posted by Stephen Furley (Member # 1277) on 11-04-2002, 02:55 PM:

SR*D is twenty six frames in advance of picture. I think, but I'm not absolutely certain that the others are printed in level sync with the picture, I'm sure Karen can answer for DTS, do we have any SDDS experts here? I recently read some material on CDS which stated that this system was in level sync.

It doesn't matter what type of readers you have for SR*D, the track is still in the same place, it just uses a longer delay the higher up the reader is, I don't know what the maximum is.

Kinoton now make a dual guage (35/16mm) projector where the 16mm (analogue) soundhead is above the gate and the sound is delayed by the necessary amount. Within certain limits it no longer matters where you put the sound head with digital systems. I assume the Kinoton machine digitises the analogue 16mm signal, I can't imagine that they delay it several seconds by analogue means.

Posted by Michael Schaffer (Member # 1204) on 11-04-2002, 05:03 PM:

The SDDS S-side (sound side) track is in editorial sync with the picture while the P-side (picture side) track is 17 frames behind.
I think the Dolby Digital data is 26 perforations ahead of the analogue sound. If I am not mistaken here, that means the data are 21 frames (analogue offset) + 6 frames (26 perforations) = 27 frames ahead. But I am not 100% sure.
Yes, the Kinoton FP38E 16mm soundhead uses a difital delay which can be programmed to various projector speeds and offsets. But it is very difficult to get the sound really in sync with the picture as a tiny variation of the loop size will affect the sync since the frames on 16mm are so small. The other disadvantage is that the machine has the douser and the soundhead coupled. So if you open the douser at the first frame, you will miss the first couple of seconds of audio as the soundtrack is long past the penthouse reader by that time. We have spend a lot of time with the guys from Kinoton at the Berlin Film Festival to solve that problem. In the end, we activated the douser/soundhead when the sound start approached the soundhead and covered the lens with a piece of cardboard until the first frame arrived at the picture gate...
Apart from that, the FP38E is a very good projector with variable speeds and an optional reverse which comes in very handy at the festival as they always want to see the first 1-2 minutes of each film before the screening starts. After the test run, I could reverse the film in the projector. I liked that.

edit - I also think dts timecode is in sync with the picture. But I am not sure either.
But the SDDS information is solid.

Posted by Christopher Seo (Member # 7) on 11-04-2002, 05:44 PM:

According to an older SDDS manual, it's actually the S track that lags the P track by 17 frames. Didn't even say where the P track was in regard to the picture. I assume the only reason for this is to reduce the chance of both tracks being damaged at the same point in the audio.

Posted by Michael Schaffer (Member # 1204) on 11-04-2002, 05:54 PM:

You are right there. I was writing from memory. Anyway, the P track is in editorial sync with the picture and the S track is 17 frames behind.
Now we got it right. Yes, the two tracks are offset to each other as each track contains a backup channel for the opposite track.

Posted by Steve Guttag (Member # 268) on 11-04-2002, 06:59 PM:

The FP-38E 16mm sound issues are long since in the past (years). The exciter lamp turns on with the motor and the sound output tracks with the changeover.

Now they just need to get it right with the 35mm LED issue. They have them tracking with the changeover rather than the motor...silly Germans.

Steve

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

Posted by Michael Schaffer (Member # 1204) on 11-04-2002, 07:03 PM:

The FP-38E 16mm sound issues are long since in the past (years). The exciter lamp turns on with the motor and the sound output tracks with the changeover.

But not on the first reel! Or has Kinoton America come up with a solution that the original developers haven`t seen? It wouldn`t surprise me.

Posted by Karen Hultgren (Member # 395) on 11-04-2002, 07:27 PM:

Mark,

The DTS offset is the distance of the DTS reader to the projector's picture gate. The DTS reader must be placed ahead of the picture gate.

To determine the offset value, thread film and count frames from the DTS reader's lens to the picture aperture. Multiply that number by 1.25 and subtract one. If you do not get a whole number, round it off to the closest whole number and put that into the offset setting.

This informmation is in all DTS cinema manuals. The manuals are posted on our free online tech center at here click on 'techcenter' to get access.

Karen at DTS
khultgren@dtsonline.com

Posted by Tim Reed (Member # 137) on 11-04-2002, 07:45 PM:

Karen, I think he was wanting to know how much it is offset on the film (during recording) from the actual picture that a particular time code frame syncs with.

Posted by Steve Guttag (Member # 268) on 11-04-2002, 08:45 PM:

Actually, it was Kinoton America that forced the change that is on all new FP-38E projectors...so yes the first reel is fine too. There is a relay on the backplane of the 16mm sound system...it's job is to disconnect the output of the delay from the "party line". The relay only allows sound to play IF the changeover is open. Since the exciter lamp is turned ON the moment the "FWD" button is pressed, the delay starts filling immediately (with the wind up noise and such as the flywheel comes up to speed). By the time you open the douser on the first reel (or changeover) the buffer is already ready and waiting...when the douser open button is pressed, all is well.

This has been in effect for about 2-years now.

Steve

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

Posted by Michael Schaffer (Member # 1204) on 11-05-2002, 04:24 AM:

That is sad news in a way. We had the problem at the festival in February 01, and again in February of this year. When obviously the American office had already found a solution. Well, it doesn`t really surprise me since there isn`t even much communication between the mother house in Munich and the Berlin office.
When the FP30E came out, there were sound problems because the electronic intermittent transports very quickly and the film hadn`t completely calmed down at the soundhead. We had them install another roller between intermittent and soundhead on our projectors at Sony Center. Munich was still shipping projectors without that roller for a long time after we already had the solution.

Posted by Steve Guttag (Member # 268) on 11-05-2002, 07:57 AM:

For some reason, I thought they had posted the mod at Kinoton America. Instead, if you go here

You will be instructed to contact them for the modification.

If you obtain the current drawing on the 16mm backplane, (it ends in /01) the modifications should become somewhat apparant. Or you could simply email Kinoton America.

Steve

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

Posted by Mark J. Marshall (Member # 1409) on 11-05-2002, 09:22 AM:

Holy cow! Wow. I'm sorry I missed my own conversation here! :-)

Anyway, yes, I was looking for the offsets on the FILM itself. So far, it looks like we have:

SR*D: 26 frames ahead of picture.

DTS: In sync --- ?

SDDS: P Track is in sync with picture, S Track is 17 frames behind picture.

CDS: In sync - we think.

Thanks!
Mark

Posted by Michael Schaffer (Member # 1204) on 11-05-2002, 11:14 AM:

CDS is not in sync...anymore

Maybe the manual the manual available here contains the info you want? I am too lazy to check myself.

Posted by John Pytlak (Member # 331) on 11-05-2002, 12:36 PM:

The Kodak Cinema Digital Sound (CDS)picture/sound displacement was 0 frames:
here CDS Specifications

------------------
John P. Pytlak, Senior Technical Specialist
Worldwide Technical Services, Entertainment Imaging
Research Labs, Building 69, Room 7525A
Rochester, New York, 14650-1922 USA
Tel: +1 585 477 5325 Cell: +1 585 781 4036 Fax: +1 585 722 7243
e-mail: john.pytlak@kodak.com
Web site: http://www.kodak.com/go/motion

Posted by Karen Hultgren (Member # 395) on 11-06-2002, 11:51 AM:

Mark, please look at my earlier posting. It describes how to set the offset (sync) on the DTS players.

Let me know if you have any questions.

Karen at DTS
khultgren@dtsonline.com

Posted by Karen Hultgren (Member # 395) on 11-06-2002, 11:53 AM:

If you mean where does the timecode start, it is placed 4 perfs after the audio sync pop.

Karen at DTS
khultgren@dstonline.com

Posted by Mark J. Marshall (Member # 1409) on 11-06-2002, 12:01 PM:

quote:
it is placed 4 perfs after the audio sync pop

OK, so if I follow you correctly, that means if analog audio is 19.5 frames ahead of picture (I think that's right) and DTS is 4 perfs AFTER that, then the DTS timecode is ofset from the picture by 18.5 frames in advance of the picture?

Mark

Posted by Jeffry L. Johnson (Member # 453) on 11-06-2002, 12:23 PM:

The analog sound track is 21 frames ahead of picture.

DTS is in sync with the picture.

Posted by Karen Hultgren (Member # 395) on 11-07-2002, 11:42 AM:

Yes, DTS is in sync with the picture. DTS timecode starts 4 perfs after the sync pop. The analog track starts after the sync pop as well.

Karen at DTS
khultgren@dtsonline.com

Posted by Mark J. Marshall (Member # 1409) on 11-08-2002, 08:14 AM:

Karen,

I'm sorry... Is it in sync with the picture on the film, or 4 perfs (1 frame) after the picture? I'm writing up technical documentation on sound formats, and I want it to be correct.

And what about 70mm DTS?

Thanks,
Mark

Posted by Karen Hultgren (Member # 395) on 11-11-2002, 01:38 PM:

The DTS timecode is in sync with the picture.

Karen at DTS
khultgren@dtsonline.com

Posted by Ken McFall (Member # 845) on 11-11-2002, 03:22 PM:

Can anyone confirm that analogue is 20 frames in advance of the picture and not 21 as suggested. Standard leaders have the number and star relationship 20 frames. I've had this discussion before and was able to confirm it was 20 frames, its in one of the BKSTS manuals but I've not got one in front of me right now.

Posted by John Pytlak (Member # 331) on 11-11-2002, 03:31 PM:

SMPTE 40-1997 specifies:
_____________________________________________________________________
3 Longitudinal picture-audio displacement

3.1 The audio record on the film shall be displaced
longitudinally from the center of the corresponding
picture by a distance of 21 frames ±
1/2 frame in the direction of film travel during
normal projection.

3.2 Although picture and audio are correctly synchronized
with a displacement of 21 frames ± 1/2
frame on the film, normal playback of motion
pictures occurs in theaters where the relatively
slow speed of sound means that the audio
should precede the picture at the screen if subjectively
correct synchronism is to be achieved
in the middle of the theater (see annex A).

Annex A (informative)
Explanatory notes
In the average theater, it is necessary to emit the sound
pulses before the corresponding picture frame is positioned
in the aperture. Since sound travels approximately 1100 ft
per second or about 50 ft per frame during the normal
projection rate of 24 frames per second, the projectionist
can place the sound and picture in synchronization in the
theater where he wishes by varying the length of the threading
path in the projector.

For example, if the positioning of frame 21 at the scanning
point brings the corresponding picture and sound to the
screen and the speaker at the same instant, then positioning
frame 20 at the scanning point would give synchronism at
about 50 ft from the screen.
_____________________________________________________________________

The SMPTE sells copies of standards, including a CD-ROM containing .pdf files of all the motion picture standards. Highly recommended for any theatre service engineer:
here SMPTE Standards

Posted by Ken McFall (Member # 845) on 11-11-2002, 03:44 PM:

Hi John,

just found a reference to picture/sound sync in the 1979 BKSTS manual, can't find it in the last issue, and it clearly states 20 frames? So whats going on here. I can't imagin the BKSTS is wrong and I don't doubt your information.

Also why are standard leaders setup with sync marks 20 frames apart.

Has there been some change in recent years?

I seem to recall this question came about while discussing the correct lacing loops on the FP20.

Posted by John Pytlak (Member # 331) on 11-11-2002, 04:12 PM:

I think some of the leaders have the marks at 20 frames offset, assuming an average seating distance of 50 feet (1/24 second for sound to travel) from the screen. But on the print itself, the picture the gunshot should be 21 frames from the "bang" on the track.

Posted by Jeffry L. Johnson (Member # 453) on 11-11-2002, 06:45 PM:

For additional information about the 21 frame optical sound offset read page 10 of H-50-3, Film Notes for the Reel People "Projection Practices and Techniques."

Posted by John Pytlak (Member # 331) on 11-11-2002, 08:01 PM:

Here's a link to issue H-50-3 of Kodak's Film Notes for Reel People: here

Posted by Carl Martin (Member # 1146) on 11-12-2002, 06:46 AM:

another consequence of having the 20-frame offset on the leader is that the same leader can be use to sync up mag sound (assuming 16-frame intervals in the countdown). 28 frames in the opposite direction + 20 frames = 48 frames is divisible by 16.

i've never dealt with mag though so there could be something i'm missing. like maybe the leader ought to have mag stripes on it?

carl

Posted by Scott Norwood (Member # 30) on 11-12-2002, 07:04 AM:

Older versions of the academy leader actually have "mag sound start" markings at the beginning. I've never run mag, either, so I'm not sure exactly how this would line up, but the marking is there....