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Let me know if you have any questions.

quote:

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it is placed 4 perfs after the audio sync pop

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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?

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?

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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

------------------
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: here

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?

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