Simple laboratory setup for obtaining sound spectrograms

Abstract

A technique for obtaining sound spectrograms using common laboratory equipment is described. The procedure is to record the signal on a tape loop and reproduce it repeatedly. The tape output is fed successively through different bandpass filters to the intensity electrode of an oscilloscope. The oscilloscope beam is triggered by a 2-kc pulse inserted ahead of the signal. After each repetition of the signal, the filter selector and the vertical position of the trace on the scope are advanced by one step. An oscilloscope recording camera registers the spectrogram under time exposure. The Performance of this setup is improved by using an AVC circuit to accommodate the wide range of intensities encountered in speech within the recording range of the oscilloscope and film.