The effect of head-induced interaural time and level differences on speech intelligibility in noise

Abstract

The effect of interaural time delay (ITD) and acoustic headshadow on binaural speech intelligibility in noise was studied. A free-field condition was simulated by presenting recordings, made with a KEMAR manikin in an anechoic room, through headphones. Recordings were made of speech, reproduced in front of the manikin, and of noise, emanating from seven angles in the azimuthal plane, ranging from 0° (frontal) to 180° in steps of 30°. From this noise, two signals were derived, one containing only ITD, the other containing only headshadow. Speech-reception thresholds for sentences in noise for a group of normal-hearing subjects showed that for noise azimuths between 30° and 150°, the gain due to ITD lies between 3.9 and 5.1 dB, while the gain due to headshadow ranges from 3.5 to 7.8 dB. A second experiment with similar stimuli, presented monaurally or with a 20-dB interaural level difference, indicated that for noise with only headshadow, the gain relies on the ear presented with the most favorable signal-to-noise ratio, but decreases when the noise presented to the other ear becomes relatively loud.