The international photographer (Jan-Dec 1934)

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Twenty-six The INTERNATIONAL PHOTOGRAPHER February, 1934 Motion Picture Sound Recording HIS chapter continues the discussion that was begun last month of the permanent monitoring equipment and its functioning. The first installment on monitoring described the potentiometer that is connected in the output circuit of each microphone ; and explained the manner in which it is operated to control the flow of speech current from the microphone. The path of the speech current was traced through the potentiometer and the monitoring, or "booster", amplifier ; and it is at the output of the amplifier that this chapter picks up the dicussion. The Main Volume Control Between the output of the booster amplifier and the transmission line linking it with the main recording amplifier is a potentiometer of the same type that is connected in the output of each microphone. This potentiometer is known as the main volume control, and has for its purpose the regulation of the overall amount of speech energy that is recorded ; whereas the individual mixer potentiometers are provided only for controlling the amount of speech current coming from each microphone. If several microphones are employed for recording, as is done for orchestrations, the potentiometers connected to the individual microphones can each be adjusted to provide the correct proportion of speech current and left at that adjustment; the main volume control alone being used to control the amount of energy fed to the recording amplifier. The Volume Indicator Meter The main volume control is mounted in a small cabinet with a slanting front, which is placed on top of the monitor desk. Mounted on the panel with the main volume control is a meter known as the volume indicator extension meter. This meter is connected in series with another similar meter in the amplifier room, the two meters being shunted across a resistance in the plate circuit of the vacuum tube in the volume indicator circuit. The input circuit of this vacuum tube is connected through a special tapped transformer to the output of the main recording amplifier in the amplifier room. The two meters read exactly alike and indicate at all times the electrical level of the speech current that is being recorded. The meters act like alternating current voltmeters, measuring the voltage that is applied to the recording device. The indications of a volume indicator meter are purely relative; and the monitor man judges the amount of sound that is being recorded by watching the continual deflecting, or "kicking", of the pointer. The pointer moves under the influence of each sound that is picked up by the microphones and transmitted to the main amplifier, the amplitude of the pointer movement being governed by the volume of the sound causing it. Only the peak values of the sounds, and not their average values, are indicated by the meter. To prevent overloads of the recording system, the meter pointer is not permitted to deflect beyond a certain predetermined point on the meter scale, the point usually being at about fifty. The volume indicator meter, being an electrical device, is not prone to the errors that afflict the human ear. It is almost impossible for even an experienced monitor man to record sound at the same average level day after day without the aid of an electrical device to supplement his hearing. The monitor horns assist the monitor man in Chapter VI By Charles Felstead Associate Editor securing the most pleasing balance of the various musical instruments in making orchestrations, in checking the recording quality of actors' voices, and in detecting the presence of any interfering noises that may be picked up by the microphones, such as the noise produced by camera gears. But the volume of sound that is recorded is determined by observing the deflecting of the volume indicator meter pointer. It is extremely difficult to monitor successfully without the aid of both monitor horns and meter. Signal and Communication Equipment Standing beside the cabinet that holds the main volume control is a duplicate cabinet, on the panel of which are mounted the six colored lenses of the signal system and four key switches. Two of the key switches operate lights of the signal system ; the other two switches provide the monitor man with controls for the relays that transfer the monitor horns from the direct recording circuit to either of the photo-electric cell circuits. This arrangement permits the monitor man to check the light valves on the two film recording machines during the making of each take to assure himself that they are operating properly and the sound is being recorded on the film. This subject will be discussed in a later chapter. Besides the four switches, there is a push button on the signal panel. The pressing of this button turns on a small public address system, the horn of which is mounted on the wall of the sound stage. This allows the monitor man to give directions to the microphone man and other persons on the stage without recourse to the more inconvenient intercommunicating telephone. The public ad A motoring setup that is somewhat unusual, because it provides for the control of as many as twelve microphones. It is advantageous to have two men at the controls when scoring music. Courtesy Paramount Pictures. Please mention The International Photographer when corresponding with advertisers.