Speech Modifications to Increase the Intelligibility of Vocal Messages Broadcast by Driving Assistance Systems Intended For Hearing-Impaired Drivers

The purpose of the AIDA (Automobile Intelligible pour Déficients Auditifs - Intelligible automobile for hearing impaired) project is to develop speech modifications tools to increase the intelligibility of voice messages broadcast by driving assistance systems embedded in personal vehicles. The target audience for this project is people suffering from mild and moderate hearing loss. This article presents an approach to increase the intelligibility of natural speech signals by signal processing methods based on filtering and dynamic compression. The magnitude of the filter was defined from a global SII (Speech Intelligibility Index) optimisation method in a driving situation incorporating hearing loss via the use of a hearing loss simulator. The effect of these speech modifications on intelligibility level was assessed using a word test on ten hearing-impaired subjects. The results show a significant increase in the speech reception threshold (SRT) in two different in-car noises. The SRT was shifted by about –9 dB to –11 dB depending on the in-car noise compared to unmodified words with identical sound pressure levels.