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NEW AND OLD ASPECTS OF THE ORIGINS OF 96-CYCLE DISTORTION*
J. O. BAKER AND R. O. DREW**
Summary. — The work of previous investigations is reviewed and correlated with the results obtained in a comprehensive study of 96-cycle distortion due to the presence of sprocket-holes adjacent to the sound-track. This distortion has been known for some time. Much improvement has been made by the adoption of the magnetic-drive recorder, the non-slip printer, and the rotary stabilizer sound-head for the purpose of overcoming the problem of slippage.
Recording sound on doubly perforated film will introduce 96-cycle disturbances of both amplitude and frequency modulation because of the film flexure and possible variations of film speed at the sprocket-hole rate.
Processing sound records on doubly perforated film will introduce a 96-cycle hum and amplitude modulation depending upon the processing technic.
Printing sound records on doubly perforated film introduces 96-cycle hum and disturbances of both amplitude and frequency modulation, due to film flexure and variations of film speed at sprocket-hole rate.
Reproducing sound records on doubly perforated film introduces 96-cycle disturbances because of film flexure.
Since it has been proved that the presence of the sprocket-holes adjacent to the soundtrack is the source of all 96-cycle distortion, and the omission of the sprocket-holes entirely eliminates this distortion, it becomes obvious that singly perforated film should be used throughout all phases of sound recording and reproduction if complete freedom from 96-cycle distortion is to be obtained.
Substantial improvement can be realized if the singly perforated film is employed only for the original negative, master positive, and re-recorded negative, and doubly perforated film for the release prints. The use of singly perforated film throughout all phases has a decided advantage of providing additional space, without affecting the picture dimensions for a double-width sound-track or two sound-tracks, one for control or other purposes.
Types of 96-Cycle Distortion. — If a film is given a uniform exposure, as, for example, in the recording of an unmodulated density track, it is not uncommon when the film is run through a reproducing machine to hear a faint tone of 96-cycle pitch. This means that there are
* Presented at the 1941 Spring Meeting at Rochester, N. Y.; received June 5, 1941.
** RCA Manufacturing Co., Indianapolis, Ind.
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