An Improved Chromatic Stroboscope
Robert W. Young, Allen Loomis · The Journal of the Acoustical Society of America · 1937
A multiple-disk stroboscope is described which permits direct measurement of audio-frequencies from 32 to 4070 cycles/sec. The light source is controlled by the sound whose frequency is to be measured. Twelve disks are permanently interconnected by suitable gearing to rotate at speeds corresponding very closely to the frequencies of the twelve chromatic notes within an octave of the equally tempered scale, the disk pattern having a separate sector ring for each of the seven octaves of the range. The basic driving speed of the stroboscope disks is controlled by an electrically maintained tuning fork. In addition, accurately measurable variation of the basic speed over a small range is provided to permit measurement of any frequency in terms of cents deviation from some note of the equally tempered scale based on A =440 cycles/sec. (One cent represents a frequency difference less than 0.06%.) Applications of the device are described illustrating its usefulness in musical problems of tuning and intonation. Its special value is pointed out for cases in which effects of an audible comparison tone are undesirable.