I N T R 0 D U C T I 0 N
It is essential to strictly follow these operating instructions in order to obtain satisfactory
results and avoid apparatus trouble. Everything in this book should therefore be carefully
studied and thoroughly understood. If anything in it is not clear to you, consult our
representatives, who will be glad to explain.
It is of the greatest importance to observe strict cleanliness in the handling of the film and
all parts of the equipment, as explained in detail later in these instructions.
Cases have occurred where persons having some radio experience have experimented with the
equipment and made changes and substitutions. Not only is this expressly forbidden in the
contract by which the equipment is leased to the theatre, but also there will almost certainly
be serious ill effects on the quality of reproduction and the life of the equipment.
The main purpose of this equipment is to reproduce speech, music or incidental sounds in
connection with moving pictures in a manner so realistic that the effect is practically
equivalent to having the speakers, artists or occurrences actually present, every sound being
heard at the same moment that the action accompanying it is seen on the screen. A further use is
to accompany feature pictures with specially recorded cued music and effects, known as a
synchronized score, so that every scene has music and effects appropriate to it, and when the
scene changes, any corresponding change in the character of the sound accompaniment is
accurately and automatically made at the same moment. Hence the two applications mentioned are also collectively called synchronous reproduction.
General Principles of the Equipment
Two methods of recording are employed. In one method, the sound record is on a disc similar to a
phonograph record, and this is therefore called the disc method. It is used by Vitaphone. In the
other method, the sound record is photographed on the film. This is called the film; method. It
is used by Movietone. A house can be equipped for showing productions made by either method or
both, the only difference lying in the apparatus used at the projector.
The first step in synchronous reproduction is to generate a small electric current whose
variations correspond to the sound waves forming the voice or music that was recorded. Depending
on which of the two previously mentioned methods of recording was used, this current is obtained
as follows (Figs.1 & 2):
(1) With the disc method, the current comes from an electrical reproducer playing on a disc
record; these records are similar to the best types of phonograph record except that they are
much larger and run at about half standard speed; this enables each record to play throughout a
whole reel. The film used with the disc record, called a synchronized film, is similar to an
ordinary film, except that one frame at the beginning is specially marked to give the starting
(2) With the film method, the sound record consists of a band about 1/8" wide, called the sound
track, which runs down one side of the film and consists of microscopic lines (Fig-3). The
spacing of these lines at each point depends on the pitch of the sound which was recorded at
that moment. The difference in density of the lines depends on the loudness of the sound - that is, the greater