Abstract
IT may be of interest to give a preliminary account of what I believe to be a new method of producing acoustic spectra. The method, which is to employ the striations on “variable-density” sound-film as a diffraction grating for monochromatic light, permits an instantaneous separation of sound into its components which is analogous to the directness with which a spectroscope analyses light. If sound-film is modulated by a pure tone, a visual appreciation of frequency is clearly possible, the diffraction angle increasing with frequency. It might be anticipated that in the case where numerous frequencies are present, the diffraction pattern might contain a confused series of combination frequencies, after the manner of the ghosts which appear with imperfect diffraction gratings possessing extraneous periodicities. A further complication might be expected from the fact that the range of frequencies recorded on the film extends over at least seven octaves, producing a correspondingly great overlapping of orders of spectra.
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BROWN, D. Sound-Films as Diffraction Gratings for the Visual Fourier Analysis of Sound-Waves. Nature 140, 1099 (1937). https://doi.org/10.1038/1401099a0
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DOI: https://doi.org/10.1038/1401099a0
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