🚀 go-pugleaf

speaking as a filmmaker in a former life, i've found
that a professional film editor knows when something
is even 1 frame out of sync (that's at 24 fps for film).

in my experience, a general audience can't tell the 
difference at 1 frame out; they may sense something is wrong
at 2 frames out, but don't know quite what; and at 3 or more
frames out, everybody seems to know what's wrong. 

on a 16mm film projector, the optical sound track is ahead
of the picture by some number of frames; the advance is 20 
for 35mm, i'm not sure about 16mm. this is because the film
must be travelling at a constant velocity when it goes over 
the audio playback head, but the film must be held still for 
picture projection. every 1/48 of second the projector's 
shutter opens and displays a frame frozen in the gate. then 
the shutter closes and the film advances to the next frame 
during the following 1/48 of a second, while the screen is black.
several spring-loaded rollers help to smooth out the jitter 
in the film's velocity before it hits the sound head.

note that there must be exactly 20 frames between the gate and 
the sound pickup to play synchronized sound. when threading, the 
size of the bottom loop is the most critical factor. if the loop
is too small, the sound is early; if the loop is too big, the sound
is late. thanks to armies of amateur operators, whole generations 
of elementary school students have grown up watching 16mm films 
out of sync for this very reason. perhaps this explains a certain
insensitivity to this problem among general audiences ... :)

as to whether early or late makes a difference, i'm told
that being early with sound is much worse than being late;
and logically that would seem to make sense; but in my 
experience it didn't matter. i have known experts who could 
tell pretty quickly whether sound was ahead or behind of 
the pix, but most people don't have a clue about the 
direction of the delay when it's under 1/2 second. i know
i didn't; i always had a tough time syncing up wild tracks 
where there was no slate. back and forth, back and forth 
i'd go ...

try editing film on a Steenbeck flatbed some time. since you
have separate sound and picture tracks, it's real easy to 
slip frames back and forth to experience the effect.

--Russ
rs05@gte.com