A New Analyzer for the Audible Frequency Range

This instrument was designed for comparatively rapid analysis of sound spectra produced by musical instruments. It is a heterodyne analyzer using an intermediate frequency of 20 kilocycles per second. The filter is a magnetostrictive resonator of very low decrement capable of distinguishing between two frequency components only forty cycles per second apart while differing by some fifty decibels in amplitude. The amplitudes are measured by a logarithmic voltmeter controlling a cathode‐ray oscillograph which records their relative magnitude, calibrated directly in decibels, on a strip of photographic paper. The recording camera is geared to the oscillator which furnishes the heterodyne frequency in such a way that the audible range up to 10,000 cycles per second may be swept out in a comparatively short time. Every effort has been made to reduce the duration of transients in the system. Preliminary tests indicate that a complete analysis may be made in about twenty seconds.