Using active echo cancellation to minimize stimulus reverberations during hearing studies conducted with the auditory brain response (ABR) technique

Andrij Z Horodysky,Richard W Brill,Mark R Patterson,Bruce W Deffenbaugh

doi:10.4236/jbise.2010.39116

Abstract

Because of the physical properties of water as sound conducting medium and the proximity of tank walls, creating an anechoic environment underwater is both technically difficult and expensive to implement. Conducting hearing studies of aquatic animals can therefore be challenging due to stimulus reverberations. To address this issue, we developed MATLAB scripts capable of pre-compensating acoustic stimuli resulting in location-specific echo cancellation. Our procedures are specifically designed for hearing studies conducted with the auditory brain response (ABR) technique. Broadband white noise is used to characterize the system response and the digitized acoustic signal subsequently used to generate an acoustic inverse file capable of cancelling reverberations. Echo cancellation is nearly perfect, although location-specific. The effectiveness of echo cancellation diminishes with distance from test subject and hydrophone (or microphone) used to create the pre-compensated signal. This distance must be minimized and should preferably be less than 5 cm. The spectral composition of the sound signal is not greatly affected, however. We have successfully used the procedure during hearing studies of several fish species, including yello- wfin tuna (set in italics). ABR experiments on the latter were done at sea aboard an oceanographic research vessel, a highly echoic environment.

Highlights

In studies of hearing in terrestrial organisms, anechoic chambers are often used so that the response of the subject to the source stimulus, and not echoes, can be accurately assessed [1]
We developed MATLAB scripts capable of pre-compensating acoustic stimuli resulting in location-specific echo cancellation
Our procedures are designed for hearing studies conducted with the auditory brain response (ABR) technique

Summary

INTRODUCTION

In studies of hearing in terrestrial organisms, anechoic chambers are often used so that the response of the subject to the source stimulus, and not echoes, can be accurately assessed [1]. Researchers interested in either the hearing abilities or the effects of sound on the behavior and health of aquatic organisms [10] are often forced to choose less expensive measures such as placement of the test aquarium in an anechoic room [11] Even this solution, does not eliminate echoes within the tank itself. Our active echo cancellation procedure makes ABR experiments more readily doable outside of an anechoic environment It permits a wider range of organisms to be investigated, including aquatic organisms that are difficult (or impossible) to transport to shore side tanks, maintain in captivity, or both

THEORETICAL CONSTRUCT

IMPLEMENTATION USING MATLAB SCRIPTS

USING THE ACTIVE EHCO CANCELLATION TECHNIQUE

Findings

LIMITATIONS