“TALKIE" PICTURES

Manawatu Herald, Volume LI, Issue 4472, 1 July 1930, Page 4

“TALKIE" PICTURES

WESTERN ELECTRIC EXPERIMENT ON SPEED SYNCHRONI-

ZATION PERFECT

Tlie following article serves to further instance the extent of the experiments being carried on at the Western Electric works in the general scheme of dovopolmenl in the recording and reproducing of sound.

•Synchronization between sound recording and film is required for all types of sound pictures. In the Western Electric system it is secured by electrical methods for the recording apparatus and, for the reproducer, by mechanically coupling the picture projection machine and the sound record. With satisfactory synchronization thus secured, there still, remains, however, the problem of speed control. Musical pitch varies directly with frequency or rate of vibration. The faster the record is rotated the higher the pitch of the sound given out. In order, therefore, that (he reproduced music* may be of the same pitch ns that recorded, the sound must run at an assigned speed, and to keep the pitch from varying during the playing of the record, this speed must be prevenIcd from changing. To attain these ends, the speed of the driving motors must he accurately controlled. PRECISION IX SYNCHRONIZATION.

In determining how nearly constant this should be held, the criterion is the smallest pitch change that is noticeable, and it has been found that abrupt variations are more readily perceived than slow ones. A good musical ear will detect sudden changes in pitch produced by a change in speed of only one-half of one per cent, To make sure, therefore, that a discernable change in pitch never arises, speed regulation better than one half of one per cent, is required at all times. Western Electric bad perfected this control motor unit, but, as further allowances seemed desirable to provide a suitable factor of safety, a regulation of twotenths of one per cent, was agreed upon. An exhaustive survey showed I hat no commercial governing mechanism was available which would meet the requirements. The most suitable was probably the governor used with ordinary phonographs. This governor applies friction, as the speed increases, and. il becomes increasingly difficult, because of maintenance difficulties, lo design a satisfactory governor, of this type for the larger motor required to drive both the projecting machine and turntable. A completely now design seemed the only satisfactory

course. The nature of the problem and the difficulties to bo overcome are perhaps most readily brought out by considering a simple lly-ball governor controlling the speed of .a. steam engine. Rotation tends to make the flv move outward, due to the centrifugal force. As they move out, however, they pull up a sliding collar and this action, through a system of levers, closes the steam valve supplying the engine, or in some other manner decreases the supply of steam and, the engine slows down. The tendency of the balls to fly outward is opposed by their weight, so that there is a definite equilibrium position for each speed.

As a. result of this the engine will run at a. given speed for only one load. A load greater than this will require a wider valve opening- so as to admit more steam, and this in iurn will require a tower position of the fly-halls to allow it. This necessary drop in speed to allow a wider valve opening may be reduced, however, by removing the position of the pivoting lever to the left. This changes the lever ratio so that smaller and smaller movements of the sliding collar will produce greater and greater valve openings. Inherently, however, some speed change must be permitted in order that the valve may be moved to accommodate the new load. To enable the engine to run at one speed regardless of the load requires an udditinoal mechanism that will admit enough more steam to the engine to carry the increased load at the desired .speed.

EXPE NSIVE MACHINERY NECESSARY. '

When, however, they sensitivity of the governor is made too great by moving the lever pivot too far to the left, or when the additional mechanism is added to make the engine run at the same speed, an unstable condition is brought about. Under these conidl ions the engine, at each action of the governor, tends to overshoot its mark, either not attaining equilibrium speed at ail, or reaching it only after several oscillations. This instability had to be overcome — and to overcome it special apparatus was designed which cannot be made perfectly except in great numbers, as the expense of such accurate and scientific machinery is terrific. A mil is one thousandth of an inch—much less than the thickness of a sheet of paper, yet t;o the makers of Wlestern Electric sound equipment a mil is as important as a mile. The fifty years of experience of Western Electric is the only tiling that makes such accuracy possible, and the research work which is being carried on, the ibenefits of which may not be. felt by exhibitors for a few years, is only possible in an organisation employing some 283,000 employees.