A Simplified Audiospectrometer

Abstract

A relatively small array of equipment is described that permits the measurement of the power spectrum of irregular or discontinuous sounds, including speech. A sample of speech, or any other sound, is recorded on a loop of magnetic tape that can be played back over and over again. Repetitions of the sample are independent of the variability of the talker. The output of the tape playback is fed through a system of cascaded, variable electronic filters; the output of the filters is fed to a square-law integrator circuit, which has been adapted from Rudmose et al.; and the output pulses of the integrator activate an electronic scaler. Scaler counts are proportional to the energy and an absolute value of energy is obtained from a calibration in counts per second. Flexibility is enhanced by the fact that the number and the width of frequency bands measured may be determined or changed at will. From an apparatus point of view it is shown that spectral analysis of speech need not require special components, which must be purchased for that purpose alone, but rather mostly employs equipment that is standard in most experimental laboratories. Increase in the time required for measurement is offset by a reduction in the size and complexity of equipment. Preliminary measurements in which both octave and equal-mel bands were used yield results that are in substantial agreement with those of previous workers.