I N T R 0 D U C T I 0 N

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General

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.

Caution

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.
Purpose 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 point.

(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