Synchronization and Speed Control of Synchronized 

 Sound Pictures ^ 



By H. M. STOLLER 



Synopsis: The reproduction of the synchronized sound picture of today 

 presents no serious problem of synchronization, for this factor has been 

 practically eliminated by the perfection of electrical means for reproducing 

 sound with equipment which may be coupled mechanically to the picture 

 projector. 



The important problem of the present day, in connection with the 

 reproduction of synchronized sound pictures, is the provision of suitable 

 means for maintaining a constant speed of the sound reproducing mechanism 

 in order that the pitch of the sound being reproduced may not suffer any 

 sudden change which would be sensed by a good musical ear. Control 

 circuits using vacuum tubes with a frequency bridge as a speed standard 

 with provision for manual variable speed control are described and explained 

 for use with both A.C. and D.C. motors. Remote synchronization permitting 

 the recording of pictures and sound simultaneously on equipment located 

 some distance apart is obtained by a modification of the Michalke electric 

 gear system. 



WHEN Thomas A. Edison gave a demonstration of his talking 

 motion pictures nearly sixteen years ago one of his chief 

 problems was proper synchronization between his acoustic phonograph 

 and the motion picture projector. It was then necessary to locate 

 the phonograph behind the screen in order to make the sound appear 

 to come from the picture. A system of belts and pulleys running 

 from one end of the theater to the other was used to secure synchro- 

 nization with the projector in the booth. 



The development of the electrical reproducer has made it possible 

 to locate the turntable and reproducing mechanism in the projection 

 booth permitting a direct mechanical coupling between it and the 

 projector. The horns are located behind the screen and electrically 

 connected by wires with the electrical reproducer. 



Thus there is no problem of synchronization in reproducing except 

 to set the needle on the disc at the proper point before starting. 

 However, such mechanical coupling between the projector and sound 

 recorder (either of the disc or film type) makes it necessary to provide 

 very close speed regulation on the projector motor, since variations in 

 speed produce proportional changes in the pitch of the sound. 



This paper will describe the speed regulating system employed in 



reproducing and the synchronization system used in recording. 



1 Presented before Society of Motion Picture Engineers at Lake Placid, New 

 York, September 24, 1928. 



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