> > > >

1954-55 Theatre Catalog, 12th Edition, Page 287 (251)

1954-55 Theatre Catalog, 12th Edition
1954-55 Theatre Catalog
1954-55 Theatre Catalog, 12th Edition, Page 287
Page 287

1954-55 Theatre Catalog, 12th Edition, Page 287

Perspecta Stereophonic Sound

Study of the Basic Principles and the Equipment Required to Obtain Stereophonic Sound From a Single Optical Track

Stereophonic sound can now be recorded on and reproduced from a single optical track of any existing variety. In fact, during the past several months, hundreds of theatres have been equipped to show film with stereophonic sound recorded by this method. This accomplishment, Perspecta Stereophonic Sound, is the result of an idea conceived by C. Robert Fine and the development of the practical equipment by Fairchild Recording Equipment Company, under the direction of Ray F. Crews. The system was quickly accepted by the motion picture industryis major producers as the standard for stereophonic sound.

Standard Equipment Used

The basic intent of the development was to provide stereophonic sound on standard film without modification of the lilm nor modincation of the projector in which it is used. This means that all film productions made by the Perspecta method can be played on all existing optical sound reproducing systems with no changes whatsoever. If the theatre is not equipped for directional sound, no consideration need be given to the use of the film. However, if stereophonic reproduction is desired, and the theatre has magnetic-type sound-reproducing equipment, the only additional equipment, required is an itintegrator." In those houses in which stereophonic equipment has not been installed, it is necessary, of course, to add three power amplifiers and three horn systems.



Theatre Equipment Products Mgr. Fairchild Recording Equipment Co.

BRIEF: Many exhibitors . . . because of financial . . . physical . . . or personal reasons . . . did not install magnetic stereophonic sound in their theatres . . . The fact that this new method of sound presentation was an iiextraii which helped bring in customers . . . however . . . made directional sound a valuable asset . . . A solution to this problem appears to be offered by the Perspecta stereophonic sound system . . . which makes it possible to obtain. directional sound from a single optical track . . . using standard projection. equipment and procedures.

This article . . . prepared by one of the men responsible for the development of the equipment needed . . . is an attempt to clear up some of the confusion found concerning such things as how the system works . . . what is needed . . . the theory . . . and also information on installation . . . and maintenance.

How Perspecta Works

In the actual reproduction of stereophonic sound, the audience is conscious primarily of the difference in sound intensity from different directions. For example, when a voice originates near the left side of the screen, it is identified

A FRONT (left) and rear (right) View of the power supply. and integrator unit necessary in order to obtain the optical stereophonic sound.

as coming from the left only because it is louder from the left speaker than sound emanating from the center and right speakers. The Perspecta sound method of recording is particularly adaptable to accentuation of the volume difference effect between speakers. As a result, the most startling and spectacular effects can be realized.

To understand the basic concept of Perspecta sound, one must first remember that standard theatre sound equipment reproduces sound audible to the audience between approximately 70 and 8,000 cycles. The heart of the Perspecta sound system, then, is a speciallydesigned unit called an integrator, which accepts all sound on the optical track and then does two things: first, it separates the whole recording into two sections, one being the true audio of the program material from 63 cycles upward, and the other being control frequencies which are below 63 cycles.

The control frequencies are then separated by band-pass filters, with the result that a separate control voltage is supplied to each of the individual circuits feeding the three theatre channels. Thus, these control frequencies present on the Perspecta sound track accurately govern the distribution of sound to the three theatre horn systems. To be specific, letls assume that the action and sound on the left side of the stage is to be accentuated. The studio mixer raises the volume of the 30-cycle control signal being recorded and reduces the volume of the 35- and 40-cycle carriers by the desired amounts. As the action and sound
1954-55 Theatre Catalog, 12th Edition, Page 287