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WESTERN ELECTRIC RECORDING SYSTEM 521
studio should have a very low reverberation time. It is practically impossible to meet open air conditions but by treating the floor and the walls of the studio properly a sufficient approach to the ideal condition may be obtained. The floor should be solid, preferably consisting of several inches of solid concrete covered by some vibration absorbing material such as felt upon which may be laid a wooden floor. The walls and ceiling should be treated with sound absorbing material but it is extremely important that a proper choice be made of this material in that it should have, as far as possible, uniform sound absorbing qualities over a frequency range of from 50 to 7000 cycles. Almost every studio is an individual problem which must be engineered to meet the necessary requirements. In such a studio it is, of course, possible to modify the acoustic conditions as desired in the design of sets.
The Studio in Use. — The sounds incidental to the motion picture are picked up in the studio, amplified, and transmitted to film and wax machines. These recording machines are operated in exact time relation with the camera motors and certain identification marks are provided for purposes of synchronization.
In recording sound, air vibrations in the studio are first translated into electrical variations which in the case of film recording are converted into light variations and in the case of wax recording are converted into mechanical variations. In order to operate either a film or a wax recording machine it is necessary to amplify the sound energy picked up in the studio in some cases several billion times before sufficient power is available. This must all be done without introducing extraneous noise or without impairing the frequency characteristic of the system used in recording sounds. The frequency characteristic of the recording system from the output of the condenser microphone in the studio to the input of the electrical recorders is substantially uniform between 50 and 7000 cycles.
The proper design and control of the apparatus necessary to provide all of this amplification without introducing serious defects has been a problem of no mean magnitude. The best engineering solution at the present time indicates the desirability of associating an amplifier with the condenser transmitter which picks up the sound. In the monitoring room, which will be discussed later, the output of several of these condenser transmitter amplifiers are coupled together, each having an individual volume control. A booster amplifier is provided at this point, the output of which goes to the