Sound motion pictures : from the laboratory to their presentation (1929)

2o8 SOUND MOTION PICTURES The programme is rehearsed until satisfactory arrangement of the microphones, and of all amplifier gain, is effected. In recording, it is of course necessary that the microphones be placed outside the camera field or that they be properly masked. The intensity of sound varies inversely with the square of the distance. The problem of suitable position of the microphone is of utmost importance, especially during recording of soft sounds. When one is recording large orchestras and complex musical organizations, the sound must be properly balanced and carefully adjusted through the use of the monitor system. This monitor system is a replica of the standard reproducing system and this enables one to judge at all times how the reproduced record should affect the ear. In some recording work a number of pick-ups are used in order to combine and adjust various currents through the use of the mixing panel. Acoustic treatment in the walls of the monitoring room secures the reverberating characteristics of the theatre, and the monitoring level is so adjusted that the mixer operator hears the same loudness that he would wish to hear from the theatre horns. With no film in the machine a complete rehearsal is held. When results are satisfactory the film is loaded, the cameras and the sound recorders are interlocked, and starting marks are made on all film by punches or light flashes. A light signal from the recording room warns the studio stage, which, after lighting up, signals back its readiness to begin. The machine operator starts the cameras and sound recorders and signals the stage to commence. During the recording the mixer operator monitors the record through the light valves, thereby assuring himself that no record is lost. In recording for disks the usual procedure is to use a disk from one inch to two inches thick and from thirteen