The Sound Prism

The methods of sound analysis used at present are classified into those in which an analyzing operation is performed upon a photographic record of the wave and those in which the wave is analyzed as it is being produced. It is pointed out that the methods of the first group are very laborious and that those of the second group are slow in action, making them unsuitable for analyzing sounds of relatively short duration such as those produced by persons. The need for a device to perform a rapid analysis is indicated. A new rapid acting heterodyne wave analyzer called the "Sound Prism" is described and its operation is illustrated. The frequency spectrum is repeatedly traced on a translucent screen by a spot of light at such a rate that persistence of vision allows the eye to see the path of the spot as a steady line on the screen. The frequency spectrum is thus shown almost instantaneously so that changes in the spectrum may be continuously followed by the eye as the composition of the sound changes and the ear hears the change in quality. Sample records of analyses are given and a brief description of the work already done in the field of musical tone analysis is presented. The limitations of the sound prism in regard to resolution and speed are discussed and plans for further development are outlined.