Acoustic Properties of Tongue Clicks used for Human Echolocation

Abstract

In active human echolocation, it is common for visually impaired persons to produce tongue click signals for extracting information from the physical environment around them. The purpose of this paper is to provide a comprehensive dataset of original detailed experimental data on human tongue clicks. The methods used for analysis are described in order to encourage further work to complement the data, which is available online and open for contributions. Series of six different click signals have been recorded from blind persons in an anechoic room. The different click signals all resemble damped oscillations and have in common that the dominant frequency content is located between 1,000 Hz and 8,000 Hz. The standard deviation in click series of the broadband click sound level is between 2.2 and 4.3 dB. The total duration of the clicks, which is mainly determined by the drop-time, ranges between 2.0 ms and 10.0 ms, for a 20 dB decay range. Average standard deviations of 57% in rise-time and 32% in drop-time have been found. The horizontal and vertical directivity of the tongue clicks show a close agreement with literature data from speech signals, but click signals are generally more directive. The minimum and maximum deviations in the 1/3 octave bands from 1,250 Hz to 4,000 Hz are less than 6 dB, for 0 to 120 deg. azimuth, and for –27 to 127 deg. elevation.