Film-Tech Forum ARCHIVE: Missalignment of pix and soundtrack

This is topic Missalignment of pix and soundtrack in forum Film Handlers' Forum at Film-Tech Forum ARCHIVE.

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Posted by Frank Angel (Member # 248) on 08-16-2004, 08:10 AM:

I would like to know if I am making the wrong assumption when I see in the leader of many prints, the Picture Start frame and the four frames of the soundtrack that also say Start don't line up, sometimes by as much as two or three sprocket holes. Shouldn't they be exactly lined up? And when you see that they are not, do you need to make any compensation in threading? I would imageing a sprocket or two would not impact lip sync, but I would think that aligning the sound neg and the pic neg would be very important and they rarely, if ever, would not be absolutely "sprocket hole accurate." Even a single hole off just seems a bit sloppy to me.

And isn't that hole that is punched in the very beginning of the leader used to physically align the two negatives to the unexposed film? I thought the negs both have holes where they are in perfect alignement and then the lab tech punches a whole in the raw stock, both pic and sound neg holes are use to align to the unexposed film so both passes are in sync. So if that is the case, that there is a physical reference in all three elements, how is it that so many prints seem to have this misalignment problem?

Posted by John Pytlak (Member # 331) on 08-16-2004, 08:43 AM:

Standard SMPTE 40 specifies 21 +/- 1/2 frame displacement between the center of the picture frame and the analog track.

Printers used for release prints usually have both a picture head and a sound head, so the printing is done in one pass.

Here is the ACVL Manual:

http://www.acvl.org/manual.htm

quote:
Recommended Procedures for
Motion Picture and Video Laboratory Services

ONLINE TABLE OF CONTENTS

Working with your ACVL Laboratory
Film Laboratory Services
ACVL Recommended Film Practices
Release Prints
Sound
Slide Duplicates and Filmstrips
Storage
Glossary of Video Terms and Definitions
World Television Standards
Business Practices

Posted by Frank Angel (Member # 248) on 08-16-2004, 12:27 PM:

OK, they so it is done in one pass, but that would seem to make it even easier to keep pix and sound in perfect alignment. Yet here are these prints where it is quite obvious that they are printed a few sprocket holes off. Is it the physical threading of the printer that makes it difficult to get them to fall exactly in correct alignment? I mean, to me, this is as important as it is for a projectionist to accurately frame the image in the aperture -- one or two sprocket holes off is unacceptable. I would think it would be even more unacceptable when marrying sound and pic in a composite print, no?

Posted by John Pytlak (Member # 331) on 08-16-2004, 01:40 PM:

On a bi-directional panel printer, the sync marks for the picture and sound negatives are lined up over the appropriate apertures on the picture and sound heads. But there is a tensioning device between the two heads for the raw stock, such that you could have a perf or two variation in the threadup, depending on the operator. Remember, this is being done in very dark conditions.

http://www.rtico.com/bhp/6131spc.pdf

quote:
Picture/Sound Negative
Synchronization:
Sync distance between picture and sound
printing apertures:
Models 6131C and 6131E -
Format Frames
35mm 21-1/2
16mm 54

Interesting that the BHP printer spec sheet says 21-1/2 frames between the heads. Wonder if this is really the case, rather than the aim of 21 frames specified in SMPTE 40?