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The problem about shrunk film
The MB51 synchronizes itself to external sources by the help
of a sprocket wheel. The encoder pulses from the sprocket
wheel encoder and the synchronisation pulses are counted and
the machine regulates the capstan speed in a way to keep the
counters equal. Shrunk film has the problem that it does not
run over the sprocket wheel because the perforation pitch
does not match the sprocket distance. The sprockets could
also damage the film when they hit between the holes. A
simple measure would be to file off the sprockets. The MB51
will trans- port the film in this case but of course not
synchronous and at wrong speed. One could think of
correcting the audio length afterwards with an editing
program, but that is no solution since the shrink-age is
likely to vary a lot during playback. The sound would never
be in lip-sync.
How L.S.D. works:
The L.S.D. modification includes:
- A special sprocket-less wheel to replace the existing
sprocketed
wheel
- A laser light barrier will be mounted nearby the
sprocketless wheel
- A microcontroller module with display will be installed
inside the
machine
The signals from the sprocketless wheel encoder and the
light barrier run into a digital signal processor which
calculates the position of a "virtual sprocket wheel". It
then generates the according output pulses which replace the
original encoder pulses from the sprocket wheel.
From the machine's point of view nothing has changed. That
means the MB51 can be operated and synchronized as usual.
The laser light barrier is sensitive enough to detect the
per- foration even in clear film. In case of damaged
perforations, sophisticated software algorithms sort out the
useless perfs and calculate their position from their
neighbours. Timecode and frame sync remain consistent up to
15 unreadable holes. A display provides some information
like actual shrinkage rate and exact speed as well as the
number of bad perforations found.
Benefits of an L.S.D. modification
The MB51 will be able to reproduce any kind of film with
shrinkage rates up to 4%. The speed is corrected during
play- back and stays perfectly in sync with external sources
like word-clock, biphase or video sync. Unlike solutions
with exchangeable sprocket wheels, L.S.D. also works when
the shrinkage rate varies during playback. Since no
sprockets exist in the whole film path, there is no danger
of damaging valuable archive material. In combination with
the specialized vinegar sound head the user gets a solution
for not only shrunk films but also films in curly and waved
condition.
Product sheet:
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