Page 34 - RD_2019-09

Figure 3. Interior View of Recording Truck. Recorder proper is at the center.
The assistant mixer operates all of the equip- sent to the "main gain amplifier", which has
ment in the portable sound truck in which the about 80 db gain and an undistorted output
recorder is located. The inside of one of these of 400 milliwatts from the pair of 71's in the
trucks is shown in figure 3. output stage.
The cable man handles the cables to the From here the sound goes into two "bridg-
various microphones, which are placed and op- ing amplifiers". One of these drives a monitor
erated by the stage man. On large sets it speaker; the other actuates the vibrator on the
sometimes becomes necessary to use more than recording machine. Bridging amplifiers have
one stage man. an output of about two watts.
Several types of microphones were in evi- In addition to the sound recording machine,
dence on the various sets, the most common the assistant mixer has control or the motion
ones being Western Electric 618-A and 630-A picture camera. The motors on both recorder
dynamics. RCA velocity mikes were seen most- and camera are electrically interlocked with a
ly where the field of acrion was stationary and "master distributor", also located in the truck.
the mike was not being swung around on a This master distributor consists of a three-
"boom". It seems that ribbon mikes are very phase generator driven by a d. c. motor. This
sensitive to vibration :tnd to swishing air cur- motor has built into it a 720 cycle a.c. wind-
rents encountered in a wind or when swing- ing, and the voltage generated by this wind-
ing the mike around to follow the action. ing is used as a speed control through a sys-
In the schematic diagram, sound is shown tem of vacuum tube relays.
entering the microphone, which transforms the After a day's work by the production crew,
sound energy to electrical energy. The micro- there are two films ready fo r processing in
phone is coupled to its respective pre-amplifier, the "film laboratory" (department B) ; one is
which is usually placed in the rear of the mix- the picture taken by the camera and the other
ing table. These pre-amplifiers have a gain of the sound film made b the recorder. For
about 45 db. technical reasons, positiYe fiLm is used for
The signal, at a level controlled by the sound recording and panchromatic negative
mixer, is then sent to the recording truck, film for the cameras.
which is located near the set. On the T,wen- In the film processin laboratory, develop-
tieth Century Fox lot, the entire recording ing of both films takes place. To obtain a
channel, with the exception of the mixing chan- finished "print" of either type (sound or pic-
nel, is tndunted in the recording tntck. ture) each must be transferred to a positive
I Tpnn reachihg the ttuck. tht> si/Zn~l is first stock. Tf sound alone i desired, one printing
• 12 •
34 REEL DEALS March 2020