Abstract
Sound analysis by a single band pass filter requires a considerable time, which is inversely proportional to the square of the frequency discrimination. Analyzers consisting of multiple resonators are cumbersome and do not cover a continuous frequency band. The paper describes a new method based on the dispersing properties of a diffraction grating analogous to those used in optical analysis and equivalent to an infinite number of resonators. The sound frequencies are modulated by a 40-kilocycle carrier, projected by a ribbon loudspeaker and reflected by a curved grating three meters long. The frequency discrimination thus attained equals that of a 125-cycle band selector; the theoretical speed of analysis approaches 0.01 second, making it possible to obtain “moving pictures” of continuously changing sound spectra.
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