Methods for improving word intelligibility of bone-conducted speech by using bone-conduction headphones

Bone-conduction (BC) headphones enable listeners to hear sounds through BC while leaving the ear canal (EC) open to pass surrounding air-conducted (AC) sound at the same time. However, BC transmission degrades the word intelligibility of BC speech, especially in noisy environments. This article examines the attenuation of higher-frequency components during BC transmission as a key characteristic that degrades speech intelligibility and proposes two methods for improving the intelligibility of BC speech by means of BC headphones. We focused on two types of BC transfer function, namely vibration of the regio temporalis (RT) and sound radiated in the EC relative to AC speech sound, and developed two methods for each (first order high-frequency emphasis (FOE) and higher-order high-frequency emphasis (HOE)) for improving the intelligibility of BC speech by compensating for the BC transmission characteristics. Speech signals in the proposed methods are filtered using four types of emphasis filter (RT-FOE, EC-FOE, RT-HOE, and EC-HOE). The results of word-intelligibility tests demonstrated that the word recognition rate, espe-cially with FOE by the inverse transfer function between RT vibration and AC speech (RT-FOE), tended to significantly increase compared to that with no emphasis. Our findings suggested that linear compensation for the attenuation of higher frequency due to BC transmission by using the inverse transfer function between RT vibration and AC speech, is effective for improving BC speech intelligibility.(c) 2023 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).