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Early Motion Picture (with sound track) frame rate and noise

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  • Early Motion Picture (with sound track) frame rate and noise

    Recently, I cleaned up a 1933 motion picture sound track. There was a continuous "whine" sound throughout the movie which was happening at 96 Hz (basically sinusoidal in shape). It turns out that the frame rate for motion pictures became standardized in 1927 at 24 frame per second (FPS). The 4th harmonic of that would be 96 Hz, and that is apparently what I observed. It was easily eliminated with a notch filter set for 96 Hz with 0.1 Octave bandwidth. My theory about why is was occurring at 96 Hz and not 24 Hz is that the camera probably had a governor that was running at a higher rate than the film itself and some of that noise transferred to the film sound track.


    Craig
    Last edited by Craig Maier; 09-10-2019, 03:58 PM.
    "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

  • #2
    As an aside, the film is titled "These Thirty Years" (actually filmed in 1934). It was produced by the Ford Motor company and documented the introduction of the V8 engine. It is sort of a docu-drama and was filmed partially in Walpack, NJ. I am cleaning the sound-track up for the Walpack Historical Society using DCForensics10.5x.

    Craig
    "Who put orange juice in my orange juice?" - - - William Claude Dukenfield

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