Competent projectionists would splice in black film equal to the number of frames damaged. Just a normal part of projection.
Ideally, the rotational pivot should be midway in its travel for maximum flexibility. It couldn't rotate 360 degrees due to the leads from the tonearm. But more than enough to compensate for subtle difficulties. And why a second set of discs were shipped with each film requiring them.
I've only experienced the Western Electric Vitaphone equipment first hand. But a vitaphone process turntable( of unknown manufacturer)that I donated to the Belfer Archive has no method of tonearm advancement. So it must have had some method of adjustment that didn't survive as it would be external to the turntable.
Maybe WE had a patent on the method.
From what I've seen in photographs and first hand WE had the best equipment in the U.S. But you paid for that privilege! And why there were other companies making sound on disc and sound on film apparatus. Most of them got a turntable drive from the intermittent flywheel on the projector head.
WE used a double shafted motor- one shaft drove the projection apparatus gearboxes- the other the turntable via extendable shafts and gearboxes.
From: Association for Recorded Sound Discussion List [mailto:[log in to unmask]] On Behalf Of George Brock-Nannestad
Sent: Thursday, June 25, 2009 2:40 PM
To: [log in to unmask]
Subject: Re: [ARSCLIST] Recording Innovations
From: Patent Tactics, George Brock-Nannestad
Hello, Bob Hodge wrote re catching up with missing film frames in a sound-on-
disc projection system so that lip sync could be maintained:
> The method of retard or advance was a special mount that allowed the tonearm
> to be advanced or retarded while the record continued at a constant speed.
> The tonearm mount rotates on a portion of the support column below the
> turntable gearbox.
> Darned clever those WE engineers!
----- yup, you could say that. However, a bit of calculation demonstrates
that there is a limit to the total number of frames for a whole reel that
could be corrected.
The records ran at 33 1/3 rpm, which calculates to 200 degrees per second.
This corresponds to 24 frames. This means that you have to move the pivot of
the tonearm 8.33 degrees for each frame lost, or a right angle (give or take)
for 11 frames lost. If the WE equipment was good and the film reasonable I
suppose this never happened. So, we may conclude that if the tonearm mount
was swivelable over a right angle they would be home free. However, the
differential that was used by other makers was continuously variable and did
not have to be reset when a new reel (corresponding to a new disc) was