Richardson's handbook of projection (1930)

1202 HANDBOOK OF PROJECTION FOR Victor speed regulator, which is supplied with the motor. The speed used for recording on standard phonograph records is 78 revolutions per minute. It therefore is essential that the speed of each turntable be carefully regulated and maintained at exactly 78 r.p.m., for the same reason that standard speed must be maintained in synchronous disc reproduction, namely, to avoid distortion of the sound by operation at other than the recorded speed. The ordinary phonograph speed indicator is not employed, as it is not sufficiently accurate, and the use of a stroboscope, or revolution counting with a watch, is therefore necessary. The speed should be carefully regulated and tested once each day. The electrical reproducer unit used for pick-up with each turntable is the same as that used in the synchronous disc equipment, the supporting arm and mounting being, of course, somewhat different. IMPORTANT. — In using an equipment of this type, it is, of course, frequently desirable to select only part of a record for reproduction, which may involve beginning elsewhere than at the start of the record, or finishing the selection before the conclusion of the record, or taking a piece from the middle of the record. To facilitate picking the right points on the record for this purpose, a graduated scale is attached to the reproducer arm. Then by playing the record through and observing the points on the graduated, scale at which the desired selection begins and ends, it becomes a simple matter to play this selection whenever desired by moving the reproducer out over the record until the scale indicates that the beginning point of the selection has been reached, and then setting down the needle on the record. A lever is provided which, when depressed, raises the repro