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

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.