COMPLETE REPRODUCING SYSTEMS 313 



at the high frequencies. The following attenuator controls the overall 

 volume. The output of the amplifier feeds the light modulator and the 

 monitoring system. By means of the optical system and light modulator 

 the electrical variations are recorded on the film into the corresponding 

 variations in density (termed variable density recording) or in area (termed 

 variable area recording). The monitoring system is also connected to the 

 output of the recording amplifier. An equalizer is used to adjust the 

 frequency characteristic to simulate that of the ultimate reproduction. 

 If the monitoring is carried out in a room a loud speaker is used. When 

 the monitoring and mixing is carried out on the set, head phones are used 

 for monitoring. 



The negative record is sent to the laboratory and developed. Then 

 positive records of both the sound and the picture are printed from the 

 sound and picture negatives. These positive records are then developed 

 and are ready for reproduction in a theatre. 



The variable density or variable area record is reproduced in the theatre 

 by pulling it past a slit illuminated by a light and a suitable optical sys- 

 tem. The resultant variations in light, due to the variable density or 

 variable area on the film, fall upon the photoelectric cell and are converted 

 into the corresponding electrical variations. These are then amplified and 

 fed to equalizers and filters. A low pass filter is used to cut out the ground 

 noise due to film above the upper limit of reproduction. An equalizer is 

 used to adjust the frequency characteristic to that suitable for the best 

 reproduction in the theatre. The attenuator is used for adjusting the 

 level of reproduction. The output of the power amplifier feeds the stage 

 loud speakers and monitoring loud speaker. The monitoring loud speakers 

 and the attenuator are located in the projection booth. As a matter of fact, 

 the entire system, save for the stage loud speakers, is located in the pro- 

 jection booth. A dividing network and a two channel loud speaker systenj 

 are shown in Fig. 12.20. Of course, any type of suitable loud speaker 

 described in Chapter VIII may be used. The action of a sound motion 

 picture reproducer in a theatre has been discussed in Sec. 12.25 and will 

 not be repeated here. 



In some cases, the original record is re-recorded and additional sound is 

 added. For example, in certain dialogue sequences it may be desirable 

 to add incidental music to heighten the artistic effects. In this case the 

 dialogue is recorded first. Then this record is reproduced on a system 

 similar to the theatre reproducer. The orchestra is picked up on the 

 standard recording system. The two outputs are mixed and fed to the 

 modulator and a new negative record is made. 



