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1950 MAGNETIC SOUND CONVERSION 317
relationship between flutter rate and its minimum perceptibility will permit much larger values at high rates. For example, flutter at 96-cycle rate may be nearly 10 times that at rates between 5 and 10 cycles for equivalent perceptibility.
The addition of magnetic recording and monitoring facilities to the RA-1231 film recorder is shown by Fig. 1. The magnetic head at the drum position is shown as the light-colored circular object located in front of the recording drum and bearing upon the overhanging edge of the film which has the magnetic coating on the inside surface. An identical magnetic head used for monitoring may be seen at the right just above the film and located in the film loop between the recording drum and the lower right-hand filter roller. Both heads are adjustable for azimuth and track position and the recording head mounting is pivoted so that it is pressed against the film with a controlled pressure at all times to compensate automatically for factors such as film curl. This arrangement maintains proper contact at all times between the surfaces of the head and the film coating, and its motion is well damped to maintain stability and damp out small transient motions such as those produced by a splice passing the head. The recording-head mounting is also provided with a device for retracting the head and holding it away from the film to prevent contact during photographic recording, particularly in the case where the modulator is moved toward the front of the machine to record on the outside edge of the film for producing direct-positive sound tracks without the necessity of reversing the direction of motion of the film in the recorder.
Good contact is maintained between the film and the monitor head by virtue of the uniform and constant tension in the film path between the two sprockets.
A magnetic erase head is also available for application to this recorder, although it is not shown in Fig. 1. When required, this head is mounted in a manner similar to the monitor head and is located to the right of the film in the path between the left-hand sprocket and the left-hand filter roller so that the film may be erased ahead of the recording point.
For magnetic recording, the film magazine is replaced by a reel adapter mounted in the same manner as a magazine. It permits the use of either the 10-in. sheet-metal reel having a 2-in. hub, or the preferred reel having an 11-in. diameter with a 4-in. hub. All magnetic conversion parts are available in kit form and may be applied