Binaural detection of sonar signals

Abstract

Standard methods of presentation of sonar signals to operators have not maximized the capabilities of the auditory system. This report describes a dichotic method of sonar signal presentation to operators based on the masking-level-difference (MLD) principle in hearing. Using a Bekesy tracking procedure, twenty-six listeners of varied experience detected recorded broadband sonar targets and low-frequency pure tones that were embedded in 100 Hz-4 kHz recorded and synthesized backgrounds. The signals were either homophasic or antiphasic and the backgrounds were always homophasic. Average detection thresholds for the antiphasic sonar signals were 5-7 dB better than their homophasic counterparts. Pure tone antiphasic detection thresholds were also 6-11 dB better than in the homophasic presentation. The sonar signals show similar MLD's as those found with speech signals. PACS numbers: 43.60.Gk, 43.30.Vh, 43.66.Pm INTRODUCTION Hirsh x described a phenomena called masking level difference (MLD) where signals 180 ø phase different at the two ears (ST) were better detected in a noise background than signals which were in phase (So) at the two ears. Since that time, numerous investigations, noted by Jeffress •' and Durlach, 3 have shown that binaural signal detection with antiphasic signals and homophasic backgrounds will yield 5-15-dB threshold improvements over homophasic signal-background conditions. A variety of different signal types have been utilized for binaural signal detection in noise. Licklider 4 showed a 5-dB improvement in detection thresholds for antiphasic speech signals masked by wide-band noise. Typical findings for detection of antiphasic tonal signals in noise range from 3-dB threshold improvement at 5 kHz to 13 dB at 200 Hz (Hirsh). x Others, Rilling and Jeffress, s have shown improved detection thresholds for antiphasic low-frequency narrow-band noise equivalent to thresholds for low-frequency pure tones, i.e., 10-14 dB.Due to the nature of a sonar operator's task, it would be advantageous for detection purposes to present sonar signals in a dichotic versus a diotic format. The present report details the detection of synthetic tonals and sonar signals embedded in synthetic and sonar noise backgrounds.

Advanced Binaural Sonar Display Using Spatial Vernier Beamforming

“…Similar laboratory manipulations using actual sonar targets in sea-noise were conducted by Kerivan (1980), who showed a 5 to 7 dB improvement under one of the conditions reported by Hirsch. In that experiment the binaural difference was created by reversing the phase of the target in the two ears, while retaining the identical phase of the noise at both ears.…”